/* ===== 色彩變數 ===== */
:root {
    /* 主色調 */
    --color-primary: #3498db;
    --color-primary-hover: #2980b9;
    --color-primary-shadow: rgba(52, 152, 219, 0.4);

    /* 強調色（出題按鈕） */
    --color-accent: #8e44ad;
    --color-accent-hover: #6c3483;

    /* 預選模式色 */
    --color-pencil: #e67e22;

    /* 危險/錯誤 */
    --color-danger: #e74c3c;
    --color-danger-hover: #c0392b;

    /* 成功 */
    --color-success: #27ae60;

    /* 深色文字 */
    --color-text-dark: #2c3e50;
    --color-text-muted: #7f8c8d;
    --color-text-hint: #999999;

    /* 背景 */
    --color-bg-page: #f0f4f8;
    --color-bg-card: #ffffff;
    --color-bg-hover: #f5f8fa;
    --color-bg-selected: #d4efff;
    --color-bg-focus: #ebf5fb;
    --color-bg-secondary: #ecf0f1;
    --color-bg-secondary-hover: #dfe6e9;

    /* 工具按鈕 */
    --color-tool-inactive: #bdc3c7;
    --color-tool-active: #2c3e50;
    --color-tool-bg-active: #ebf5fb;
    --color-tool-disabled: #dcdde1;

    /* 邊框 */
    --color-border: #bdc3c7;
    --color-border-bold: #2c3e50;

    /* 陰影 */
    --shadow-card: 0 4px 20px rgba(0, 0, 0, 0.1);
}

/* 暗色模式 */
[data-theme="dark"] {
    --color-primary: #5dade2;
    --color-primary-hover: #3498db;
    --color-primary-shadow: rgba(93, 173, 226, 0.4);

    --color-accent: #af7ac5;
    --color-accent-hover: #8e44ad;

    --color-pencil: #f0b27a;

    --color-danger: #ec7063;
    --color-danger-hover: #e74c3c;

    --color-success: #58d68d;

    --color-text-dark: #ecf0f1;
    --color-text-muted: #b2bec3;
    --color-text-hint: #95a5a6;

    --color-bg-page: #1a1a2e;
    --color-bg-card: #2d2d44;
    --color-bg-hover: #3d3d5c;
    --color-bg-selected: #1a3a5c;
    --color-bg-focus: #2a3a4c;
    --color-bg-secondary: #3d3d5c;
    --color-bg-secondary-hover: #4d4d6c;

    --color-tool-inactive: #636e72;
    --color-tool-active: #dfe6e9;
    --color-tool-bg-active: #2a3a4c;
    --color-tool-disabled: #4d4d6c;

    --color-border: #4d4d6c;
    --color-border-bold: #b2bec3;

    --shadow-card: 0 4px 20px rgba(0, 0, 0, 0.4);
}

/* ===== 基礎重設 ===== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: "Microsoft JhengHei", "PingFang TC", sans-serif;
    background: var(--color-bg-page);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: flex-start;
    padding: 20px;
    -webkit-user-select: none;
    user-select: none;
}

.container {
    background: var(--color-bg-card);
    border-radius: 12px;
    padding: 24px;
    box-shadow: var(--shadow-card);
    text-align: center;
    max-width: 500px;
    width: 100%;
}

h1 {
    color: var(--color-text-dark);
    font-size: 1.6rem;
    margin: 0;
}

/* 標題列 */
.top-bar {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 10px;
}

.top-bar h1 {
    flex: 1;
    text-align: center;
}

.top-bar-btn {
    width: 32px;
    height: 32px;
    border: 1px solid var(--color-border);
    border-radius: 6px;
    background: var(--color-bg-card);
    cursor: pointer;
    font-size: 1rem;
    line-height: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: background 0.15s;
}

.top-bar-btn:hover {
    background: var(--color-bg-hover);
}

.help-btn {
    width: 18px;
    height: 18px;
    border: 1.5px solid var(--color-text-hint);
    border-radius: 50%;
    background: transparent;
    color: var(--color-text-hint);
    font-size: 0.7rem;
    font-weight: bold;
    cursor: pointer;
    display: inline-flex;
    align-items: center;
    justify-content: center;
    margin-left: 6px;
    vertical-align: middle;
    transition: all 0.15s;
    flex-shrink: 0;
}

.help-btn:hover {
    border-color: var(--color-primary);
    color: var(--color-primary);
}

/* 說明視窗 */
.modal {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(0, 0, 0, 0.5);
    display: flex;
    align-items: center;
    justify-content: center;
    z-index: 1000;
}

.modal-content {
    background: var(--color-bg-card);
    border-radius: 12px;
    padding: 24px;
    max-width: 420px;
    width: 90%;
    max-height: 80vh;
    overflow-y: auto;
    position: relative;
    box-shadow: var(--shadow-card);
}

.modal-close {
    position: absolute;
    top: 12px;
    right: 12px;
    border: none;
    background: transparent;
    font-size: 1.2rem;
    cursor: pointer;
    color: var(--color-text-muted);
    line-height: 1;
}

.modal-close:hover {
    color: var(--color-text-dark);
}

.modal-body {
    text-align: left;
    font-size: 0.85rem;
    color: var(--color-text-dark);
    line-height: 1.6;
}

.modal-body h2 {
    font-size: 1rem;
    margin: 12px 0 6px;
    color: var(--color-primary);
}

.modal-body h2:first-child {
    margin-top: 0;
}

.modal-body ul {
    padding-left: 1.2em;
    margin: 4px 0;
}

.modal-body li {
    margin: 3px 0;
}

.lang-select {
    padding: 4px 8px;
    font-size: 0.75rem;
    border: 1px solid var(--color-border);
    border-radius: 4px;
    background: var(--color-bg-card);
    color: var(--color-text-muted);
    cursor: pointer;
    outline: none;
}

.hidden {
    display: none !important;
}

/* 操作列 */
.action-bar {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    margin-bottom: 12px;
    flex-wrap: wrap;
}

.action-bar .btn {
    padding: 6px 12px;
    font-size: 0.8rem;
    border-radius: 6px;
}

/* 滑動開關 */
.toggle-switch {
    display: flex;
    align-items: center;
    gap: 6px;
    padding: 4px 10px;
    border: 1px solid var(--color-border);
    border-radius: 6px;
    background: var(--color-bg-card);
}

.toggle-label {
    font-size: 0.75rem;
    font-weight: bold;
    color: var(--color-text-muted);
    transition: color 0.2s;
}

.toggle-label-left {
    color: var(--color-primary);
}

.toggle-switch.cell-first .toggle-label-left {
    color: var(--color-text-muted);
}

.toggle-switch.cell-first .toggle-label-right {
    color: var(--color-primary);
}

.switch {
    position: relative;
    display: inline-block;
    width: 36px;
    height: 20px;
    flex-shrink: 0;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: var(--color-primary);
    border-radius: 20px;
    transition: background 0.2s;
}

.slider::before {
    content: "";
    position: absolute;
    height: 14px;
    width: 14px;
    left: 3px;
    bottom: 3px;
    background: var(--color-bg-card);
    border-radius: 50%;
    transition: transform 0.2s;
}

.switch input:checked + .slider::before {
    transform: translateX(16px);
}

.difficulty-select {
    padding: 6px 10px;
    font-size: 0.8rem;
    font-weight: bold;
    border: 1px solid var(--color-border);
    border-radius: 6px;
    background: var(--color-bg-card);
    color: var(--color-text-dark);
    cursor: pointer;
    outline: none;
}

.difficulty-select:focus {
    border-color: var(--color-primary);
}

.btn-accent {
    background: var(--color-accent);
    color: var(--color-bg-card);
    padding: 6px 12px;
    font-size: 0.8rem;
}

.btn-accent:hover {
    background: var(--color-accent-hover);
}

.seed-input {
    padding: 6px 10px;
    font-size: 0.8rem;
    font-weight: bold;
    border: 1px solid var(--color-border);
    border-radius: 6px;
    background: var(--color-bg-card);
    color: var(--color-text-dark);
    text-align: center;
    width: 140px;
    letter-spacing: 1px;
    outline: none;
    text-transform: uppercase;
}

.seed-input::placeholder {
    color: var(--color-text-hint);
    text-transform: none;
}

.seed-display {
    font-size: 0.8rem;
    color: var(--color-text-muted);
    font-weight: bold;
    letter-spacing: 1px;
    cursor: pointer;
    padding: 6px 10px;
    border: 1px solid var(--color-border);
    border-radius: 6px;
    background: var(--color-bg-card);
    max-width: 120px;
    text-align: center;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

/* 數獨格線 */
.sudoku-grid-wrapper {
    position: relative;
    margin: 0 auto 16px;
    max-width: 450px;
    width: 100%;
    aspect-ratio: 1 / 1;
}

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    width: 100%;
    height: 100%;
    border: 3px solid var(--color-border-bold);
}

.chain-svg {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 10;
}

.cell {
    position: relative;
    width: 100%;
    height: 100%;
    border: 1px solid var(--color-border);
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: background 0.15s;
    overflow: hidden;
}

.cell:hover {
    background: var(--color-bg-hover);
}

.cell.selected {
    background: var(--color-bg-selected);
}

.cell.given {
    background: var(--color-bg-card);
    cursor: default;
}

.cell.conflict {
    background: #fde8e8;
}

.cell.conflict input {
    color: var(--color-danger);
}

.cell.given .cell-value {
    color: var(--color-text-dark);
    font-weight: bold;
}

.cell .cell-value {
    font-size: 1.4rem;
    font-weight: bold;
    color: var(--color-primary);
    position: absolute;
}

.cell .pencil-marks {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    width: 100%;
    height: 100%;
    position: absolute;
}

.cell .pencil-marks span {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.55rem;
    color: var(--color-text-muted);
    font-weight: bold;
}

/* 3x3 宮格粗邊框 */
.cell.border-right {
    border-right: 3px solid var(--color-border-bold);
}

.cell.border-bottom {
    border-bottom: 3px solid var(--color-border-bold);
}

/* 輸入題目模式：格子內的 input */
.cell input {
    width: 100%;
    height: 100%;
    border: none;
    text-align: center;
    font-size: 1.2rem;
    font-weight: bold;
    color: var(--color-text-dark);
    background: transparent;
    outline: none;
    position: absolute;
}

.cell input:focus {
    background: var(--color-bg-focus);
}

/* ===== 控制面板 ===== */
.control-panel {
    margin-bottom: 12px;
}

/* 工具列 */
.toolbar {
    display: flex;
    justify-content: center;
    align-items: stretch;
    gap: 8px;
    margin-bottom: 10px;
    flex-wrap: wrap;
}

.tool-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 2px;
    padding: 8px 10px;
    border: 2px solid var(--color-border);
    border-radius: 10px;
    background: var(--color-bg-card);
    cursor: pointer;
    transition: all 0.15s;
    min-width: 52px;
}

.tool-btn .tool-icon {
    font-size: 1.2rem;
    line-height: 1;
    transition: all 0.15s;
}

.tool-btn .tool-label {
    font-size: 0.65rem;
    font-weight: bold;
    color: var(--color-text-muted);
    transition: color 0.15s;
}

/* 常態按鈕：永遠彩色可點 */
.tool-btn-action {
    border-color: var(--color-primary);
}

.tool-btn-action .tool-icon {
    filter: grayscale(0%);
    opacity: 1;
}

.tool-btn-action .tool-label {
    color: var(--color-primary);
}

.tool-btn-action:hover {
    background: var(--color-bg-focus);
}

/* 切換按鈕：關閉時灰色，開啟時亮色 */
.tool-btn-toggle {
    border-color: var(--color-tool-inactive);
}

.tool-btn-toggle .tool-icon {
    filter: grayscale(100%);
    opacity: 0.5;
}

.tool-btn-toggle .tool-label {
    color: var(--color-tool-inactive);
}

.tool-btn-toggle.active {
    border-color: var(--color-tool-active);
    background: var(--color-tool-bg-active);
}

.tool-btn-toggle.active .tool-icon {
    filter: grayscale(0%);
    opacity: 1;
}

.tool-btn-toggle.active .tool-label {
    color: var(--color-tool-active);
}

/* hover */
.tool-btn:hover {
    transform: scale(1.04);
}

/* 停用狀態（適用於任何按鈕） */
.tool-btn.disabled {
    border-color: var(--color-tool-disabled);
    cursor: not-allowed;
    opacity: 0.4;
}

.tool-btn.disabled:hover {
    border-color: var(--color-tool-disabled);
    transform: none;
}

.tool-btn.disabled .tool-icon {
    filter: grayscale(100%);
    opacity: 0.3;
}

/* 提交按鈕特殊樣式 */
.tool-btn-submit {
    border-color: var(--color-success);
}

.tool-btn-submit .tool-icon {
    filter: grayscale(0%);
    opacity: 1;
}

.tool-btn-submit .tool-label {
    color: var(--color-success);
}

.tool-btn-submit:hover {
    background: #eafaf1;
}

/* 預選按鈕啟用時 */
.tool-btn-toggle.pencil-active {
    border-color: var(--color-pencil);
    background: #fef5e7;
}

.tool-btn-toggle.pencil-active .tool-icon {
    filter: grayscale(0%);
    opacity: 1;
}

.tool-btn-toggle.pencil-active .tool-label {
    color: var(--color-pencil);
}

/* 數字面板 */
.number-buttons {
    display: flex;
    justify-content: center;
    gap: 4px;
    flex-wrap: nowrap;
}

.num-btn {
    width: 38px;
    height: 38px;
    font-size: 1.1rem;
    font-weight: bold;
    border: 2px solid var(--color-primary);
    border-radius: 8px;
    background: var(--color-bg-card);
    color: var(--color-primary);
    cursor: pointer;
    transition: all 0.15s;
    flex-shrink: 0;
}

.num-btn:hover {
    background: var(--color-primary);
    color: var(--color-bg-card);
}

.num-btn.active {
    background: var(--color-primary);
    color: var(--color-bg-card);
    box-shadow: 0 2px 8px var(--color-primary-shadow);
}

.num-btn-erase {
    border-color: var(--color-danger);
    color: var(--color-danger);
}

.num-btn-erase:hover,
.num-btn-erase.active {
    background: var(--color-danger);
    color: var(--color-bg-card);
    border-color: var(--color-danger);
}

/* 數字已填滿 */
.num-btn.num-complete {
    opacity: 0.25;
    pointer-events: none;
}

/* 底部 */
.footer-bar {
    margin-top: 12px;
}

.footer-spacer {
    height: 32px;
}

/* 按鈕通用 */
.btn {
    padding: 10px 22px;
    font-size: 0.95rem;
    font-weight: bold;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: transform 0.1s, opacity 0.2s;
}

.btn:active {
    transform: scale(0.96);
}

.btn-primary {
    background: var(--color-primary);
    color: var(--color-bg-card);
}

.btn-primary:hover {
    background: var(--color-primary-hover);
}

.btn-secondary {
    background: var(--color-bg-secondary);
    color: var(--color-text-dark);
}

.btn-secondary:hover {
    background: var(--color-bg-secondary-hover);
}

.btn-danger {
    background: var(--color-danger);
    color: var(--color-bg-card);
}

.btn-danger:hover {
    background: var(--color-danger-hover);
}

.btn-small {
    padding: 8px 14px;
    font-size: 0.85rem;
}

/* 訊息 */
.message {
    margin-top: 10px;
    font-size: 0.9rem;
    min-height: 1.4em;
    color: var(--color-danger);
    font-weight: bold;
}

.message.success {
    color: var(--color-success);
}

.message.highlight {
    font-size: 1.3rem;
    padding: 12px;
    background: #eafaf1;
    border: 2px solid var(--color-success);
    border-radius: 8px;
    animation: pop 0.4s ease;
}

@keyframes pop {
    0% { transform: scale(0.8); opacity: 0; }
    50% { transform: scale(1.05); }
    100% { transform: scale(1); opacity: 1; }
}

/* ===== 鍊推理 ===== */

/* 輔助高亮：含有選中數字的格子 */
.cell.highlight-same {
    background: color-mix(in srgb, var(--color-primary) 25%, transparent);
}

/* 輔助高亮：預選數中匹配的數字 */
.cell .pencil-marks span.pencil-highlight {
    color: var(--color-bg-card);
    background: var(--color-primary);
    border-radius: 50%;
    font-weight: bold;
}

/* 鍊節點標記：圈起來的預選數 */
.pencil-marks span.chain-node {
    border-radius: 50%;
    width: 80%;
    height: 80%;
    display: flex;
    align-items: center;
    justify-content: center;
}

/* 數字按鈕在鍊模式下的禁用 */
.num-btn.chain-disabled {
    opacity: 0.2;
    pointer-events: none;
}

/* ===== 響應式 ===== */

/* 桌面：隱藏手機元素 */
@media (min-width: 521px) {
    .mobile-only {
        display: none !important;
    }
}

/* 手機：隱藏桌面元素 */
@media (max-width: 520px) {
    .desktop-only {
        display: none !important;
    }

    body {
        padding: 8px;
    }

    .container {
        max-width: 100%;
        padding: 12px;
        border-radius: 8px;
    }

    h1 {
        font-size: 1.3rem;
        margin-bottom: 8px;
    }

    .sudoku-grid-wrapper {
        max-width: 100%;
    }

    .cell .cell-value {
        font-size: 1.1rem;
    }

    .cell .pencil-marks span {
        font-size: 0.45rem;
    }

    /* 工具列：均分寬度填滿整排 */
    .toolbar {
        gap: 4px;
    }

    .tool-btn {
        flex: 1;
        min-width: 0;
        padding: 10px 4px;
    }

    .tool-btn .tool-icon {
        font-size: 1.3rem;
    }

    .tool-btn .tool-label {
        font-size: 0.6rem;
    }

    /* 數字鍵：均分寬度填滿整排 */
    .number-buttons {
        gap: 3px;
    }

    .num-btn {
        flex: 1;
        min-width: 0;
        height: 48px;
        font-size: 1.2rem;
    }

    .btn {
        padding: 8px 16px;
        font-size: 0.85rem;
    }
}

@media (max-width: 360px) {
    .cell .cell-value {
        font-size: 0.9rem;
    }

    .cell .pencil-marks span {
        font-size: 0.4rem;
    }

    .num-btn {
        height: 42px;
        font-size: 1rem;
    }

    .tool-btn {
        padding: 8px 4px;
    }

    .tool-btn .tool-icon {
        font-size: 1.1rem;
    }
}