.sudoku-solver-page .toolbar {
    display: flex;
    flex-wrap: wrap;
    gap: 8px;
    padding: 15px 0;
    justify-content: center;
    align-items: center;
}
.sudoku-solver-page .toolbar .btn {
    display: flex;
    align-items: center;
    justify-content: center;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s;
}
.sudoku-solver-page .toolbar .btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
}
.sudoku-solver-page .toolbar .btn:active {
    transform: translateY(0);
}
.sudoku-solver-page .toolbar .btn-icon-square {
    width: 72px;
    height: 48px;
    padding: 0;
}
.sudoku-solver-page .toolbar .btn-icon-square .btn-svg {
    width: 24px;
    height: 24px;
}
.sudoku-solver-page #btn-next-step .icon-execute {
    display: none;
}
.sudoku-solver-page #btn-next-step.btn-success .icon-next {
    display: none;
}
.sudoku-solver-page #btn-next-step.btn-success .icon-execute {
    display: block;
}
.sudoku-solver-page .toolbar .btn-icon {
    font-size: 16px;
}
.sudoku-solver-page .btn-primary {
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
}
.sudoku-solver-page .btn-success {
    background: linear-gradient(135deg, #28a745, #20c997);
    color: white;
}
.sudoku-solver-page .btn-info {
    background: linear-gradient(135deg, #17a2b8, #6610f2);
    color: white;
}
.sudoku-solver-page .btn-warning {
    background: linear-gradient(135deg, #ffc107, #fd7e14);
    color: #333;
}
.sudoku-solver-page .btn-secondary {
    background: linear-gradient(135deg, #6c757d, #495057);
    color: white;
}
.sudoku-solver-page .btn-outline {
    background: linear-gradient(135deg, #e8ecff, #d4dbff);
    color: #667eea;
    border: 1px solid #667eea;
}
.sudoku-solver-page .btn-outline:hover {
    background: linear-gradient(135deg, #667eea, #5a6fd6);
    color: white;
}
.sudoku-solver-page .btn-danger {
    background: linear-gradient(135deg, #dc3545, #c82333);
    color: white;
}
.sudoku-solver-page .toolbar .btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none !important;
    box-shadow: none !important;
}
.sudoku-solver-page .mobile-only {
    display: none;
}
.sudoku-solver-page .dropdown {
    position: relative;
    display: inline-block;
}
.sudoku-solver-page .dropdown-arrow {
    font-size: 10px;
    margin-left: 4px;
}
.sudoku-solver-page .dropdown-menu {
    display: block;
    position: absolute;
    bottom: 100%;
    right: 0;
    margin-bottom: 5px;
    background: white;
    border-radius: 8px;
    box-shadow: 0 -4px 20px rgba(0, 0, 0, 0.15);
    z-index: 100;
    min-width: 160px;
    overflow: hidden;
}
.sudoku-solver-page .dropdown-menu.hidden {
    display: none !important;
}
.sudoku-solver-page .dropdown-item {
    display: flex;
    align-items: center;
    width: 100%;
    padding: 10px 15px;
    border: none;
    background: none;
    text-align: left;
    font-size: 14px;
    cursor: pointer;
    transition: background 0.2s;
    color: #333;
}
.sudoku-solver-page .dropdown-item:hover {
    background: #f0f0f0;
}
.sudoku-solver-page .dropdown-item .item-icon {
    margin-right: 10px;
    font-size: 14px;
}
.sudoku-solver-page .dropdown-divider {
    height: 1px;
    background: #e9ecef;
    margin: 5px 0;
}
.sudoku-solver-page .main-content {
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
    align-items: flex-start;
}
.sudoku-solver-page .primary-panel {
    flex: 0 0 auto; 
    display: flex;
    flex-direction: column;
    gap: 20px;
    align-items: center;
    --cell-size: 41px; 
}
@media (min-width: 726px) and (max-width: 1023px) {
    .sudoku-solver-page .primary-panel {
        --cell-size: 59px; 
    }
}
@media (min-width: 1440px) {
    .sudoku-solver-page .primary-panel {
        --cell-size: 49px; 
    }
}
@media (min-width: 1920px) {
    .sudoku-solver-page .primary-panel {
        --cell-size: 55px; 
    }
}
@media (min-width: 2560px) {
    .sudoku-solver-page .primary-panel {
        --cell-size: 64px; 
    }
}
.sudoku-solver-page .sudoku-section {
    display: flex;
    justify-content: center;
}
.sudoku-solver-page .sudoku-wrapper {
    position: relative;
    display: inline-block;
    padding-left: 25px;
    padding-top: 20px;
}
.sudoku-solver-page .sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, var(--cell-size));
    grid-template-rows: repeat(9, var(--cell-size));
    gap: 1px;
    background: #333;
    border: 3px solid #333;
    border-radius: 5px;
    padding: 1px;
}
.sudoku-solver-page .cell {
    background: white;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: calc(var(--cell-size) * 0.64);
    font-weight: bold;
    color: #333;
    cursor: pointer;
    position: relative;
    transition: background-color 0.2s;
}
.sudoku-solver-page .cell:hover {
    background-color: #e8f4ff;
}
.sudoku-solver-page .cell.selected {
    background-color: #b3d9ff !important;
    outline: 2px solid #0066cc;
    outline-offset: -2px;
}
.sudoku-solver-page .cell.given {
    color: #000;
    background-color: #f0f0f0;
}
.sudoku-solver-page .cell.solved {
    color: #0066cc;
}
.sudoku-solver-page .cell:nth-child(3n) {
    border-right: 2px solid #333;
}
.sudoku-solver-page .cell:nth-child(9n) {
    border-right: none;
}
.sudoku-solver-page .cell:nth-child(n+19):nth-child(-n+27),
.sudoku-solver-page .cell:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 2px solid #333;
}
.sudoku-solver-page .candidates {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    width: 100%;
    height: 100%;
    padding: 1px;
    box-sizing: border-box;
}
.sudoku-solver-page .candidate {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: calc(var(--cell-size) * 0.24);
    font-weight: normal;
    color: #666;
    line-height: 1;
}
.sudoku-solver-page .candidate[data-value="1"] { grid-area: 1 / 1; }
.sudoku-solver-page .candidate[data-value="2"] { grid-area: 1 / 2; }
.sudoku-solver-page .candidate[data-value="3"] { grid-area: 1 / 3; }
.sudoku-solver-page .candidate[data-value="4"] { grid-area: 2 / 1; }
.sudoku-solver-page .candidate[data-value="5"] { grid-area: 2 / 2; }
.sudoku-solver-page .candidate[data-value="6"] { grid-area: 2 / 3; }
.sudoku-solver-page .candidate[data-value="7"] { grid-area: 3 / 1; }
.sudoku-solver-page .candidate[data-value="8"] { grid-area: 3 / 2; }
.sudoku-solver-page .candidate[data-value="9"] { grid-area: 3 / 3; }
.sudoku-solver-page .candidate.hidden {
    visibility: hidden;
}
.sudoku-solver-page .cell.highlight-cell {
    background-color: #fff3cd !important;
}
.sudoku-solver-page .cell.highlight-set {
    background-color: #d4edda !important;
}
.sudoku-solver-page .candidate.highlight-candidate {
    color: #0066cc;
    font-weight: bold;
    background-color: #cce5ff;
    border-radius: 3px;
}
.sudoku-solver-page .candidate.highlight-eliminate {
    color: #dc3545;
    font-weight: bold;
    background-color: #f8d7da;
    border-radius: 3px;
    text-decoration: line-through;
}
.sudoku-solver-page .candidate.highlight-chain-a {
    color: #28a745;
    font-weight: bold;
    background-color: #d4edda;
    border-radius: 3px;
}
.sudoku-solver-page .candidate.highlight-chain-b {
    color: #fd7e14;
    font-weight: bold;
    background-color: #ffe5d0;
    border-radius: 3px;
}
.sudoku-solver-page .candidate.highlight-excluded {
    color: #999;
    text-decoration: line-through;
    opacity: 0.6;
}
.sudoku-solver-page .cell.highlight-related {
    background-color: #e2e3f3 !important;
    box-shadow: inset 0 0 0 2px #6c757d;
}
.sudoku-solver-page .excluded-marks {
    position: absolute;
    top: 2px;
    left: 2px;
    right: 2px;
    bottom: 2px;
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    pointer-events: none;
    z-index: 5;
}
.sudoku-solver-page .excluded-mark {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 10px;
    color: #dc3545;
    text-decoration: line-through;
    opacity: 0.7;
}
.sudoku-solver-page .excluded-mark[data-value="1"] { grid-area: 1 / 1; }
.sudoku-solver-page .excluded-mark[data-value="2"] { grid-area: 1 / 2; }
.sudoku-solver-page .excluded-mark[data-value="3"] { grid-area: 1 / 3; }
.sudoku-solver-page .excluded-mark[data-value="4"] { grid-area: 2 / 1; }
.sudoku-solver-page .excluded-mark[data-value="5"] { grid-area: 2 / 2; }
.sudoku-solver-page .excluded-mark[data-value="6"] { grid-area: 2 / 3; }
.sudoku-solver-page .excluded-mark[data-value="7"] { grid-area: 3 / 1; }
.sudoku-solver-page .excluded-mark[data-value="8"] { grid-area: 3 / 2; }
.sudoku-solver-page .excluded-mark[data-value="9"] { grid-area: 3 / 3; }
.sudoku-solver-page .cell.error-highlight {
    background-color: #f8d7da !important;
    border: 2px solid #dc3545 !important;
    animation: sudoku-error-pulse 1s ease-in-out infinite;
}
@keyframes sudoku-error-pulse {
    0%, 100% { box-shadow: 0 0 5px rgba(220, 53, 69, 0.5); }
    50% { box-shadow: 0 0 15px rgba(220, 53, 69, 0.8); }
}
.sudoku-solver-page .col-labels {
    position: absolute;
    top: 0;
    left: 25px;
    right: 0;
    display: flex;
    height: 20px;
}
.sudoku-solver-page .col-labels span {
    flex: 1;
    text-align: center;
    font-size: 11px;
    color: #666;
    font-weight: 500;
    line-height: 20px;
}
.sudoku-solver-page .row-labels {
    position: absolute;
    top: 20px;
    left: 0;
    width: 25px;
    display: flex;
    flex-direction: column;
}
.sudoku-solver-page .row-labels span {
    height: calc(var(--cell-size) + 1px);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 11px;
    color: #666;
    font-weight: 500;
}
.sudoku-solver-page .line-overlay {
    position: absolute;
    top: 20px;
    left: 25px;
    width: calc(100% - 25px);
    height: calc(100% - 20px);
    pointer-events: none;
    z-index: 10;
}
.sudoku-solver-page .link-strong {
    stroke: #28a745;
    stroke-width: 1.5;
    fill: none;
}
.sudoku-solver-page .link-weak {
    stroke: #fd7e14;
    stroke-width: 1.5;
    stroke-dasharray: 4, 3;
    fill: none;
}
.sudoku-solver-page .arrow-strong { fill: #28a745; }
.sudoku-solver-page .arrow-weak { fill: #fd7e14; }
.sudoku-solver-page .link-strong,
.sudoku-solver-page .link-weak {
    animation: sudoku-draw-line 0.5s ease-out forwards;
}
@keyframes sudoku-draw-line {
    from { stroke-dashoffset: 1000; }
    to { stroke-dashoffset: 0; }
}
.sudoku-solver-page .hint-section {
    width: calc(25px + 9 * var(--cell-size) + 14px);
    box-sizing: border-box;
    background: #f8f9fa;
    border-radius: 12px;
    padding: 15px;
    border: 1px solid #e9ecef;
}
.sudoku-solver-page .hint-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 10px;
    padding-bottom: 8px;
    border-bottom: 2px solid #667eea;
}
.sudoku-solver-page .hint-header h3 {
    color: #555;
    font-size: 1.1em;
    margin: 0;
}
.sudoku-solver-page .step-progress {
    font-size: 13px;
    color: #667eea;
    font-weight: 600;
}
.sudoku-solver-page .hint-display {
    background: white;
    border: 1px solid #e9ecef;
    border-radius: 8px;
    padding: 15px;
    min-height: 160px;
    max-height: 200px;
    overflow-y: auto;
    font-size: 14px;
    line-height: 1.6;
    color: #333;
}
.sudoku-solver-page .hint-placeholder {
    color: #888;
}
.sudoku-solver-page .hint-placeholder p {
    margin: 4px 0;
}
.sudoku-solver-page .hint-display .technique-name {
    font-weight: bold;
    color: #667eea;
    font-size: 16px;
    margin-bottom: 8px;
}
.sudoku-solver-page .hint-display .hint-detail {
    color: #555;
}
.sudoku-solver-page .techniques-section {
    flex: 0 0 240px;
    width: 240px;
    background: #f8f9fa;
    border-radius: 12px;
    padding: 15px;
    border: 1px solid #e9ecef;
    display: flex;
    flex-direction: column;
}
.sudoku-solver-page .techniques-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 10px;
    padding-bottom: 8px;
    border-bottom: 2px solid #667eea;
}
.sudoku-solver-page .techniques-header h3 {
    color: #555;
    font-size: 1.1em;
    margin: 0;
}
.sudoku-solver-page .techniques-header-actions {
    display: flex;
    align-items: center;
    gap: 5px;
}
.sudoku-solver-page .btn-icon-only {
    background: none;
    border: 1px solid #ddd;
    border-radius: 4px;
    font-size: 16px;
    cursor: pointer;
    color: #666;
    padding: 4px 8px;
    transition: all 0.2s;
}
.sudoku-solver-page .btn-icon-only:hover {
    background: #f0f0f0;
    color: #667eea;
    border-color: #667eea;
}
.sudoku-solver-page .btn-collapse {
    background: none;
    border: none;
    font-size: 16px;
    cursor: pointer;
    color: #667eea;
    padding: 4px 8px;
}
.sudoku-solver-page .techniques-content {
    flex: 1;
    overflow: hidden;
    display: flex;
    flex-direction: column;
}
.sudoku-solver-page .techniques-actions {
    display: flex;
    gap: 6px;
    margin-bottom: 10px;
    flex-shrink: 0;
}
.sudoku-solver-page .techniques-actions button {
    flex: 1;
    padding: 6px 10px;
    font-size: 12px;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    transition: all 0.2s;
}
.sudoku-solver-page .techniques-actions .btn-enable-all {
    background-color: #28a745;
    color: white;
}
.sudoku-solver-page .techniques-actions .btn-disable-all {
    background-color: #dc3545;
    color: white;
}
.sudoku-solver-page .techniques-actions .btn-reset-order {
    background-color: #6c757d;
    color: white;
}
.sudoku-solver-page .techniques-actions button:hover {
    opacity: 0.85;
}
.sudoku-solver-page .techniques-list {
    overflow-y: auto;
    border: 1px solid #e9ecef;
    border-radius: 8px;
    background: white;
}
.sudoku-solver-page .technique-group {
    border-bottom: 1px solid #e9ecef;
}
.sudoku-solver-page .technique-group:last-child {
    border-bottom: none;
}
.sudoku-solver-page .technique-group-header {
    display: flex;
    align-items: center;
    padding: 10px 12px;
    background: #f0f0f0;
    cursor: pointer;
    user-select: none;
    transition: background 0.2s;
}
.sudoku-solver-page .technique-group-header:hover {
    background: #e5e5e5;
}
.sudoku-solver-page .technique-group-header .group-toggle {
    margin-right: 8px;
    font-size: 12px;
    transition: transform 0.2s;
}
.sudoku-solver-page .technique-group-header.collapsed .group-toggle {
    transform: rotate(-90deg);
}
.sudoku-solver-page .technique-group-header .group-name {
    flex: 1;
    font-weight: 600;
    font-size: 13px;
    color: #555;
}
.sudoku-solver-page .technique-group-header .group-count {
    font-size: 11px;
    color: #888;
    background: #ddd;
    padding: 2px 8px;
    border-radius: 10px;
}
.sudoku-solver-page .technique-group-items {
    padding: 5px;
}
.sudoku-solver-page .technique-group-header.collapsed + .technique-group-items {
    display: none;
}
.sudoku-solver-page .technique-item {
    display: flex;
    align-items: center;
    padding: 8px 10px;
    transition: background-color 0.2s;
    background: white;
    border-radius: 4px;
    margin-bottom: 2px;
    cursor: grab;
    font-size: 12px;
    min-height: 38px;
}
.sudoku-solver-page .technique-item:last-child {
    margin-bottom: 0;
}
.sudoku-solver-page .technique-item:hover {
    background-color: #f5f5f5;
}
.sudoku-solver-page .technique-item .drag-handle {
    color: #ccc;
    font-size: 12px;
    margin-right: 6px;
    cursor: grab;
    letter-spacing: -2px;
}
.sudoku-solver-page .technique-item .drag-handle:hover {
    color: #667eea;
}
.sudoku-solver-page .technique-item.dragging {
    opacity: 0.5;
    cursor: grabbing;
}
.sudoku-solver-page .technique-item input[type="checkbox"] {
    width: 16px;
    height: 16px;
    margin-right: 8px;
    cursor: pointer;
    accent-color: #667eea;
    flex-shrink: 0;
}
.sudoku-solver-page .technique-item .technique-priority {
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
    min-width: 20px;
    height: 16px;
    border-radius: 8px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 10px;
    font-weight: bold;
    margin-right: 6px;
}
.sudoku-solver-page .technique-item .technique-name {
    flex: 1;
    font-size: 12px;
    color: #333;
    line-height: 1.3;
}
.sudoku-solver-page .technique-item .technique-name-cn {
    font-weight: 600;
    color: #444;
}
.sudoku-solver-page .technique-item .technique-name-en {
    font-size: 10px;
    color: #888;
}
.sudoku-solver-page .technique-item.disabled {
    opacity: 0.5;
}
.sudoku-solver-page .technique-item.disabled .technique-name {
    text-decoration: line-through;
}
.sudoku-solver-page .technique-item.pinned {
    background: linear-gradient(135deg, #f3e5f5 0%, #e1bee7 100%);
    border-left: 3px solid #9C27B0;
}
.sudoku-solver-page .technique-group.pinned-group {
    background: linear-gradient(135deg, #faf5ff 0%, #f3e8ff 100%);
}
.sudoku-solver-page .technique-group.pinned-group .technique-group-header {
    background: linear-gradient(135deg, #f3e5f5 0%, #e1bee7 100%);
}
.sudoku-solver-page .technique-group.pinned-group .technique-group-header:hover {
    background: linear-gradient(135deg, #e8d5f0 0%, #d6aed8 100%);
}
.sudoku-solver-page .technique-item .pin-btn {
    font-size: 14px;
    width: 22px;
    height: 22px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-right: 4px;
    cursor: pointer;
    opacity: 0.3;
    transition: opacity 0.2s;
    border-radius: 4px;
}
.sudoku-solver-page .technique-item .pin-btn:hover {
    opacity: 0.7;
    background: rgba(102, 126, 234, 0.1);
}
.sudoku-solver-page .technique-item .pin-btn.pinned {
    opacity: 1;
    transform: rotate(-45deg);
}
.sudoku-solver-page .techniques-toolbar {
    display: flex;
    gap: 8px;
    padding: 8px 10px;
    background: #f8f9fa;
    border-bottom: 1px solid #e9ecef;
    position: sticky;
    top: 0;
    z-index: 10;
}
.sudoku-solver-page .techniques-toolbar .btn {
    flex: 1;
    padding: 6px 10px;
    font-size: 12px;
}
.sudoku-solver-page .techniques-toolbar .btn-xs {
    padding: 4px 8px;
    font-size: 11px;
    border-radius: 4px;
    background: #fff;
    border: 1px solid #ddd;
    cursor: pointer;
    transition: all 0.2s;
}
.sudoku-solver-page .techniques-toolbar .btn-xs:hover {
    background: #667eea;
    border-color: #667eea;
    color: #fff;
}
.sudoku-solver-page .technique-group {
    margin-bottom: 8px;
}
.sudoku-solver-page .technique-group-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 8px 12px;
    background: linear-gradient(135deg, #f8f9fa 0%, #e9ecef 100%);
    border-left: 4px solid #999;
    font-size: 13px;
    font-weight: 600;
    color: #333;
}
.sudoku-solver-page .technique-level-name {
    flex: 1;
}
.sudoku-solver-page .technique-level-color {
    width: 12px;
    height: 12px;
    border-radius: 50%;
    margin-left: 8px;
}
.sudoku-solver-page .technique-group-content {
    padding: 4px;
}
.sudoku-solver-page .technique-item[data-level] {
    border-left: 3px solid #999;
    padding-left: 8px;
}
.sudoku-solver-page .technique-item .btn-pin {
    font-size: 12px;
    width: 24px;
    height: 24px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    opacity: 0.3;
    transition: opacity 0.2s, transform 0.2s;
    border: none;
    background: none;
    border-radius: 4px;
    flex-shrink: 0;
}
.sudoku-solver-page .technique-item .btn-pin:hover {
    opacity: 0.7;
    background: rgba(102, 126, 234, 0.1);
}
.sudoku-solver-page .technique-item.pinned .btn-pin {
    opacity: 1;
}
.sudoku-solver-page .technique-item input[type="checkbox"]:disabled {
    opacity: 0.6;
    cursor: not-allowed;
}
.modal {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
}
.modal.hidden {
    display: none;
}
.modal-overlay {
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.5);
}
.modal-content {
    position: relative;
    background: white;
    border-radius: 12px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
    max-width: 500px;
    width: 90%;
    max-height: 90vh;
    overflow: hidden;
    display: flex;
    flex-direction: column;
}
.modal-content.modal-large {
    max-width: 700px;
}
.modal-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 20px;
    border-bottom: 1px solid #e9ecef;
    background: #f8f9fa;
}
.modal-header h3 {
    margin: 0;
    color: #333;
    font-size: 1.2em;
}
.modal-close {
    background: none;
    border: none;
    font-size: 24px;
    cursor: pointer;
    color: #666;
    padding: 0;
    line-height: 1;
}
.modal-close:hover {
    color: #333;
}
.modal-body {
    padding: 20px;
    overflow-y: auto;
    flex: 1;
}
.import-section,
.export-section {
    margin-bottom: 15px;
}
.import-section > label,
.export-section > label {
    display: block;
    font-weight: 600;
    color: #555;
    margin-bottom: 10px;
}
.format-select {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 10px;
}
.format-select label {
    font-size: 14px;
    color: #666;
}
.format-select select {
    flex: 1;
    padding: 8px 12px;
    border: 1px solid #ddd;
    border-radius: 6px;
    font-size: 14px;
    background: white;
}
.format-select select:focus {
    outline: none;
    border-color: #667eea;
}
#puzzle-input {
    width: 100%;
    height: 100px;
    padding: 12px;
    border: 1px solid #ddd;
    border-radius: 8px;
    font-family: monospace;
    font-size: 13px;
    resize: vertical;
    margin-bottom: 10px;
    box-sizing: border-box;
}
#puzzle-input:focus {
    border-color: #667eea;
    outline: none;
}
.import-buttons {
    display: flex;
    gap: 10px;
}
.import-buttons .btn {
    flex: 1;
}
.modal-body hr {
    border: none;
    border-top: 1px solid #e9ecef;
    margin: 20px 0;
}
.modal-body .btn {
    width: 100%;
    padding: 12px;
    font-size: 15px;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.2s;
}
.modal-body .btn:hover {
    opacity: 0.9;
}
.modal-body .btn-outline {
    background: linear-gradient(135deg, #e8ecff, #d4dbff);
    color: #667eea;
    border: 1px solid #667eea;
}
.modal-body .btn-outline:hover {
    background: linear-gradient(135deg, #667eea, #5a6fd6);
    color: white;
}
.difficulty-grid {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 12px;
}
.difficulty-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 15px 10px;
    border: 2px solid #e9ecef;
    border-radius: 10px;
    background: white;
    cursor: pointer;
    transition: all 0.2s;
}
.difficulty-btn:hover {
    border-color: #667eea;
    background: #f8f9ff;
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(102, 126, 234, 0.2);
}
.difficulty-btn:active {
    transform: translateY(0);
}
.difficulty-level {
    font-size: 14px;
    font-weight: 700;
    color: #667eea;
    margin-bottom: 4px;
}
.difficulty-name {
    font-size: 13px;
    color: #555;
}
.difficulty-btn[data-difficulty="0"] .difficulty-level,
.difficulty-btn[data-difficulty="1"] .difficulty-level { color: #28a745; }
.difficulty-btn[data-difficulty="2"] .difficulty-level,
.difficulty-btn[data-difficulty="3"] .difficulty-level { color: #5cb85c; }
.difficulty-btn[data-difficulty="4"] .difficulty-level,
.difficulty-btn[data-difficulty="5"] .difficulty-level { color: #f0ad4e; }
.difficulty-btn[data-difficulty="6"] .difficulty-level,
.difficulty-btn[data-difficulty="7"] .difficulty-level { color: #fd7e14; }
.difficulty-btn[data-difficulty="8"] .difficulty-level,
.difficulty-btn[data-difficulty="9"] .difficulty-level { color: #dc3545; }
.solve-path-list {
    max-height: 60vh;
    overflow-y: auto;
}
.path-empty {
    padding: 40px 20px;
    text-align: center;
    color: #999;
}
.path-item {
    display: flex;
    align-items: center;
    padding: 12px 15px;
    border-bottom: 1px solid #e9ecef;
    cursor: pointer;
    transition: background 0.2s;
}
.path-item:last-child {
    border-bottom: none;
}
.path-item:hover {
    background: #f5f5f5;
}
.path-item.active {
    background: #e3f2fd;
    border-left: 3px solid #667eea;
}
.path-item .step-number {
    background: linear-gradient(135deg, #667eea, #764ba2);
    color: white;
    min-width: 28px;
    height: 28px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 12px;
    font-weight: bold;
    margin-right: 12px;
    flex-shrink: 0;
}
.path-item.original .step-number {
    background: #17a2b8;
}
.path-item .step-info {
    flex: 1;
    min-width: 0;
}
.path-item .step-technique {
    font-weight: 600;
    color: #333;
    font-size: 14px;
}
.path-item .step-detail {
    font-size: 12px;
    color: #666;
    margin-top: 2px;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}
@media (max-width: 991px) {
    .sudoku-solver-page .techniques-section {
        max-width: none;
        width: 100%;
        max-height: none;
    }
    .sudoku-solver-page .techniques-list {
        max-height: 300px;
    }
}
@media (max-width: 725px) {
    .sudoku-solver-page .toolbar {
        padding: 8px 0 15px 0;
        gap: 6px;
    }
    .sudoku-solver-page .toolbar .btn-icon-square {
        width: 60px;
        height: 44px;
    }
    .sudoku-solver-page .toolbar .btn-icon-square .btn-svg {
        width: 22px;
        height: 22px;
    }
    .sudoku-solver-page #btn-reset-board,
    .sudoku-solver-page #btn-clear,
    .sudoku-solver-page #btn-solve-path {
        display: none;
    }
    .sudoku-solver-page .mobile-only {
        display: flex;
    }
    .sudoku-solver-page .main-content {
        grid-template-columns: 1fr;
        gap: 15px;
    }
    .sudoku-solver-page .primary-panel {
        --cell-size: calc((100vw - 80px) / 9);
    }
    .sudoku-solver-page .sudoku-grid {
        grid-template-columns: repeat(9, var(--cell-size));
        grid-template-rows: repeat(9, var(--cell-size));
    }
    .sudoku-solver-page .sudoku-wrapper {
        padding-left: 18px;
        padding-top: 14px;
    }
    .sudoku-solver-page .col-labels {
        left: 18px;
        height: 14px;
    }
    .sudoku-solver-page .col-labels span {
        font-size: 9px;
        line-height: 14px;
    }
    .sudoku-solver-page .row-labels {
        top: 14px;
        width: 18px;
    }
    .sudoku-solver-page .row-labels span {
        height: calc((100vw - 80px) / 9 + 1px);
        font-size: 9px;
    }
    .sudoku-solver-page .line-overlay {
        top: 14px;
        left: 18px;
        width: calc(100% - 18px);
        height: calc(100% - 14px);
    }
    .sudoku-solver-page .techniques-section {
        border-radius: 8px;
    }
    .sudoku-solver-page .techniques-content {
        max-height: 0;
        overflow: hidden;
        transition: max-height 0.3s ease;
    }
    .sudoku-solver-page .techniques-content.expanded {
        max-height: 400px;
        overflow-y: auto;
    }
    .sudoku-solver-page .btn-collapse {
        display: block;
    }
    .sudoku-solver-page .btn-collapse.expanded {
        transform: rotate(180deg);
    }
    .sudoku-solver-page .hint-section {
        width: calc(18px + 9 * var(--cell-size) + 14px);
    }
    .sudoku-solver-page .hint-display {
        min-height: 60px;
        max-height: 120px;
    }
    .modal-content {
        width: 95%;
        max-height: 85vh;
    }
}
@media (max-width: 400px) {
    .sudoku-solver-page .toolbar .btn-icon-square {
        width: 52px;
        height: 40px;
    }
    .sudoku-solver-page .toolbar .btn-icon-square .btn-svg {
        width: 20px;
        height: 20px;
    }
    .sudoku-solver-page .hint-header h3,
    .sudoku-solver-page .techniques-header h3 {
        font-size: 1em;
    }
}
.hidden {
    display: none !important;
}
.sudoku-solver-page .size-settings {
    margin-top: 30px;
    padding: 20px;
    background: #f0f4f8;
    border-radius: 12px;
    border: 2px dashed #667eea;
}
.sudoku-solver-page .size-settings h4 {
    margin: 0 0 15px 0;
    color: #667eea;
    font-size: 16px;
}
.sudoku-solver-page .size-settings .setting-row {
    display: flex;
    align-items: center;
    gap: 15px;
    margin-bottom: 12px;
    flex-wrap: wrap;
}
.sudoku-solver-page .size-settings label {
    min-width: 180px;
    font-size: 14px;
    color: #333;
}
.sudoku-solver-page .size-settings input[type="range"] {
    flex: 1;
    min-width: 150px;
    max-width: 300px;
    height: 6px;
    -webkit-appearance: none;
    background: #ddd;
    border-radius: 3px;
    outline: none;
}
.sudoku-solver-page .size-settings input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance: none;
    width: 18px;
    height: 18px;
    background: #667eea;
    border-radius: 50%;
    cursor: pointer;
}
.sudoku-solver-page .size-settings .size-info {
    font-size: 13px;
    color: #666;
    background: #fff;
    padding: 4px 10px;
    border-radius: 4px;
}
.sudoku-solver-page .btn-techniques-toggle {
    display: flex;
}
.sudoku-solver-page .techniques-sidebar-overlay {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: rgba(0, 0, 0, 0.5);
    z-index: 1000;
    opacity: 0;
    transition: opacity 0.3s ease;
}
.sudoku-solver-page .techniques-sidebar-overlay.visible {
    opacity: 1;
}
.sudoku-solver-page .techniques-sidebar {
    position: fixed;
    top: 0;
    right: -300px;
    width: 280px;
    height: 100%;
    background: #fff;
    box-shadow: -4px 0 20px rgba(0, 0, 0, 0.15);
    z-index: 1001;
    display: flex;
    flex-direction: column;
    transition: right 0.3s ease;
}
.sudoku-solver-page .techniques-sidebar.visible {
    right: 0;
}
.sudoku-solver-page .techniques-sidebar-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px;
    border-bottom: 2px solid #667eea;
    background: #f8f9fa;
}
.sudoku-solver-page .techniques-sidebar-header h3 {
    margin: 0;
    font-size: 1.1em;
    color: #333;
}
.sudoku-solver-page .btn-close-sidebar {
    background: none;
    border: none;
    font-size: 20px;
    color: #666;
    cursor: pointer;
    padding: 5px 10px;
    border-radius: 4px;
    transition: background 0.2s;
}
.sudoku-solver-page .btn-close-sidebar:hover {
    background: #e9ecef;
    color: #333;
}
.sudoku-solver-page .techniques-sidebar-content {
    flex: 1;
    overflow-y: auto;
    padding: 10px;
}
.sudoku-solver-page .techniques-sidebar-footer {
    padding: 10px 15px;
    border-top: 1px solid #e9ecef;
    background: #f8f9fa;
}
.sudoku-solver-page .btn-sm {
    padding: 6px 12px;
    font-size: 13px;
}
.sudoku-solver-page .right-panel {
    display: none;
}
@media (min-width: 1024px) {
    .sudoku-solver-page {
        display: flex;
        gap: 20px;
        align-items: flex-start; 
        width: 100%;
        max-width: 100%;
        box-sizing: border-box;
    }
    .sudoku-solver-page .main-content {
        flex: 0 0 auto; 
        min-width: 0;
        min-height: auto !important; 
        display: block; 
        height: fit-content; 
    }
    .sudoku-solver-page #btn-show-techniques,
    .sudoku-solver-page #btn-solve-path {
        display: none !important;
    }
    .sudoku-solver-page .right-panel {
        flex: 0 0 auto; 
        min-width: 240px;
        max-width: 320px;
        width: 280px;
        background: white;
        border-radius: 12px;
        box-shadow: 0 2px 12px rgba(0, 0, 0, 0.1);
        display: flex;
        flex-direction: column;
    }
    .sudoku-solver-page .btn-close-panel {
        display: none;
    }
    .sudoku-solver-page .panel-tabs {
        display: flex;
        align-items: center;
        border-bottom: 1px solid #e9ecef;
        background: #f8f9fa;
        border-radius: 12px 12px 0 0;
        padding: 0;
    }
    .sudoku-solver-page .panel-tab {
        flex: 1;
        padding: 12px 8px;
        background: none;
        border: none;
        border-bottom: 2px solid transparent;
        cursor: pointer;
        font-size: 14px;
        font-weight: 500;
        color: #666;
        transition: all 0.2s;
        white-space: nowrap;
    }
    .sudoku-solver-page .panel-tab:hover {
        color: #667eea;
        background: rgba(102, 126, 234, 0.05);
    }
    .sudoku-solver-page .panel-tab.active {
        color: #667eea;
        border-bottom-color: #667eea;
        background: white;
    }
    .sudoku-solver-page .panel-tab span {
        font-weight: normal;
        color: #999;
        font-size: 12px;
    }
    .sudoku-solver-page .panel-tab.active span {
        color: #667eea;
    }
    .sudoku-solver-page .panel-content {
        overflow: hidden;
        display: flex;
        flex-direction: column;
    }
    .sudoku-solver-page .tab-pane {
        display: none;
        overflow-y: auto;
        flex-direction: column;
        max-height: 520px; 
    }
    .sudoku-solver-page .tab-pane.active {
        display: flex;
    }
    .sudoku-solver-page .right-panel .solve-path-list {
        max-height: none;
    }
    .sudoku-solver-page .right-panel .path-item {
        padding: 10px 12px;
    }
    .sudoku-solver-page .right-panel .path-item:hover {
        background: #f0f4ff;
    }
    .sudoku-solver-page .right-panel .path-item.active {
        background: #e3f2fd;
        border-left: 3px solid #667eea;
    }
    .sudoku-solver-page .right-panel .step-number {
        min-width: 24px;
        height: 24px;
        font-size: 11px;
        margin-right: 10px;
    }
    .sudoku-solver-page .right-panel .step-technique {
        font-size: 13px;
    }
    .sudoku-solver-page .right-panel .step-detail {
        font-size: 12px;
    }
    .sudoku-solver-page #panel-techniques-list {
        overflow-y: auto;
        border: none;
        border-radius: 0;
    }
    .sudoku-solver-page .panel-techniques-footer {
        padding: 10px 12px;
        border-top: 1px solid #e9ecef;
        background: #f8f9fa;
        flex-shrink: 0;
    }
    .sudoku-solver-page .panel-techniques-footer .btn {
        width: 100%;
    }
}
@media (min-width: 1440px) {
    .sudoku-solver-page .right-panel {
        min-width: 320px;
        max-width: 400px;
        width: 360px;
    }
    .sudoku-solver-page .tab-pane {
        max-height: 480px; 
    }
    .sudoku-solver-page .panel-tab {
        padding: 14px 10px;
        font-size: 15px;
    }
    .sudoku-solver-page .right-panel .path-item {
        padding: 12px 15px;
    }
    .sudoku-solver-page .right-panel .step-number {
        min-width: 28px;
        height: 28px;
        font-size: 12px;
        margin-right: 12px;
    }
    .sudoku-solver-page .right-panel .step-technique {
        font-size: 14px;
    }
    .sudoku-solver-page .right-panel .step-detail {
        font-size: 13px;
    }
}
@media (min-width: 1920px) {
    .sudoku-solver-page .right-panel {
        min-width: 360px;
        max-width: 450px;
        width: 420px;
    }
    .sudoku-solver-page .tab-pane {
        max-height: 520px; 
    }
}
.solver-docs {
    background: var(--bg-primary, #fff);
    border-radius: 15px;
    padding: 40px 30px;
    margin-top: 20px;
    line-height: 1.8;
    color: var(--text-primary, #333);
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.05);
}
.solver-docs .docs-section {
    margin-bottom: 35px;
}
.solver-docs .docs-section:last-child {
    margin-bottom: 0;
}
.solver-docs h2 {
    color: #764ba2;
    font-size: 1.5rem;
    font-weight: bold;
    margin-top: 0;
    margin-bottom: 20px;
    padding-bottom: 10px;
    border-bottom: 2px solid var(--border-color, #e9ecef);
}
.solver-docs .docs-section:not(:first-child) h2 {
    margin-top: 35px;
}
.solver-docs h3 {
    color: #764ba2;
    font-size: 1.2rem;
    font-weight: bold;
    margin-top: 25px;
    margin-bottom: 12px;
}
.solver-docs p {
    margin-bottom: 15px;
}
.solver-docs ul,
.solver-docs ol {
    margin-bottom: 20px;
    padding-left: 25px;
}
.solver-docs li {
    margin-bottom: 8px;
}
.solver-docs a {
    color: #667eea;
    text-decoration: none;
}
.solver-docs a:hover {
    color: #764ba2;
    text-decoration: underline;
}
.solver-docs code {
    font-family: monospace;
    background: #f3f4f6;
    padding: 2px 6px;
    border-radius: 4px;
    font-weight: bold;
    color: #667eea;
}
.solver-docs .technique-list li {
    margin-bottom: 10px;
}
.solver-docs .technique-list a {
    font-weight: 500;
}
@media (max-width: 991px) {
    .solver-docs {
        padding: 25px 20px;
        margin-top: 15px;
    }
    .solver-docs h2 {
        font-size: 1.3rem;
    }
    .solver-docs h3 {
        font-size: 1.1rem;
    }
}