:root {
    /* Theme Colors */
    --app-bg: #fdfbf7;
    --sidebar-bg: rgba(255, 248, 240, 0.8);
    --glass-border: rgba(214, 59, 29, 0.2);
    --text-primary: #8b0000;
    --text-secondary: #a05a5a;
    --accent-red: #d63b1d;
    --accent-gold: #ffb400;
    --accent-hover: #b32b12;
    --success-green: #27c93f;
    --danger-red: #ff3b30;

    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(139, 0, 0, 0.08);
    --shadow-md: 0 8px 24px rgba(139, 0, 0, 0.12);
    --shadow-lg: 0 20px 40px rgba(139, 0, 0, 0.15);

    --font-family: "Noto Serif SC", "Outfit", serif;
    --font-title: "Ma Shan Zheng", cursive;
    --font-mono: 'Times New Roman', 'Courier New', monospace;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: var(--font-family);
    background-color: var(--app-bg);
    color: var(--text-primary);
    height: 100vh;
    overflow: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
    background-image: url('https://images.unsplash.com/photo-1451187580459-43490279c0fa?q=80&w=2574&auto=format&fit=crop');
    background-size: cover;
    background-position: center;
}

.app-container {
    width: 90vw;
    height: 90vh;
    max-width: 1600px;
    background: rgba(255, 252, 245, 0.85);
    backdrop-filter: blur(20px) saturate(120%);
    -webkit-backdrop-filter: blur(20px) saturate(120%);
    border-radius: 24px;
    border: 1px solid var(--glass-border);
    box-shadow: var(--shadow-lg);
    display: flex;
    overflow: hidden;
}

/* ===== Sidebar ===== */
.sidebar {
    width: 340px;
    background: var(--sidebar-bg);
    border-right: 1px solid var(--glass-border);
    display: flex;
    flex-direction: column;
    padding: 1.5rem;
    gap: 1.5rem;
    flex-shrink: 0;
    overflow-y: auto;
}

.sidebar-header {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.window-controls {
    display: flex;
    gap: 8px;
    margin-bottom: 0.5rem;
}

.dot {
    width: 12px;
    height: 12px;
    border-radius: 50%;
}

.dot.red { background: #ff5f56; border: 1px solid #e0443e; }
.dot.yellow { background: #ffbd2e; border: 1px solid #dea123; }
.dot.green { background: #27c93f; border: 1px solid #1aab29; }

h1 {
    font-family: var(--font-title);
    font-size: 2rem;
    font-weight: 400;
    color: var(--text-primary);
    letter-spacing: 0.05em;
}

.subtitle {
    font-size: 0.8rem;
    color: var(--text-secondary);
    font-style: italic;
    margin-top: -5px;
}

.highlight {
    color: var(--accent-red);
}

.controls-wrapper {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    flex-grow: 1;
}

.control-group {
    display: flex;
    flex-direction: column;
    gap: 0.6rem;
}

label {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

/* ===== Select & Textarea ===== */
.apple-select, .apple-textarea {
    padding: 10px 14px;
    border-radius: 10px;
    border: 1px solid rgba(139, 0, 0, 0.2);
    background: #fff;
    color: var(--text-primary);
    font-family: var(--font-family);
    font-size: 0.9rem;
    transition: all 0.2s ease;
}

.apple-select:hover, .apple-textarea:hover {
    border-color: var(--accent-red);
}

.apple-textarea {
    resize: vertical;
    font-family: var(--font-mono);
}

.apple-textarea:focus {
    outline: none;
    border-color: var(--accent-red);
    box-shadow: 0 0 0 3px rgba(214, 59, 29, 0.1);
}

.input-hint {
    font-size: 0.7rem;
    color: var(--text-secondary);
    font-style: italic;
}

/* ===== Mode Buttons ===== */
.mode-buttons {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 6px;
}

.mode-btn {
    padding: 8px 10px;
    border-radius: 8px;
    border: 1px solid rgba(139, 0, 0, 0.2);
    background: #fff;
    color: var(--text-secondary);
    font-family: var(--font-family);
    font-size: 0.75rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
}

.mode-btn:hover {
    border-color: var(--accent-red);
    color: var(--accent-red);
}

.mode-btn.active {
    background: var(--accent-red);
    color: #fff;
    border-color: var(--accent-red);
}

/* ===== Buttons ===== */
.apple-btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    padding: 10px 20px;
    border-radius: 12px;
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    border: none;
    font-family: var(--font-family);
}

.action-btn {
    background: var(--accent-red);
    color: white;
    width: 100%;
    box-shadow: var(--shadow-md);
}

.action-btn:hover {
    background: var(--accent-hover);
    transform: scale(1.02);
}

.danger-btn {
    background: rgba(139, 0, 0, 0.1);
    color: var(--text-primary);
    width: 100%;
}

.danger-btn:hover {
    background: rgba(139, 0, 0, 0.2);
}

.apple-btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
    transform: none;
}

/* ===== Range Slider ===== */
input[type=range] {
    appearance: none;
    width: 100%;
    background: transparent;
}

input[type=range]::-webkit-slider-thumb {
    -webkit-appearance: none;
    height: 20px;
    width: 20px;
    border-radius: 50%;
    background: var(--accent-red);
    cursor: pointer;
    margin-top: -8px;
    box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
    border: 2px solid #fff;
    transition: transform 0.1s;
}

input[type=range]::-webkit-slider-thumb:hover {
    transform: scale(1.1);
}

input[type=range]::-webkit-slider-runnable-track {
    width: 100%;
    height: 4px;
    cursor: pointer;
    background: rgba(139, 0, 0, 0.1);
    border-radius: 2px;
}

/* ===== Info Panel ===== */
.info-panel {
    background: rgba(255, 255, 255, 0.6);
    padding: 12px;
    border-radius: 12px;
    font-size: 0.9rem;
    color: var(--text-primary);
    border: 1px solid rgba(139, 0, 0, 0.1);
}

#statusText {
    font-weight: 700;
    color: var(--accent-red);
    margin-bottom: 10px;
    font-size: 0.95rem;
}

.stats-display {
    display: flex;
    gap: 16px;
}

.stat-item {
    display: flex;
    align-items: center;
    gap: 6px;
    font-size: 0.85rem;
}

.stat-label {
    color: var(--text-secondary);
    font-weight: 600;
}

.stat-value {
    color: var(--accent-red);
    font-weight: 700;
    font-size: 1rem;
}

.actions-footer {
    display: flex;
    gap: 10px;
}

/* ===== Main Stage ===== */
.visualizer-stage {
    flex-grow: 1;
    padding: 2rem;
    display: flex;
    justify-content: center;
    align-items: center;
    background: rgba(255, 255, 255, 0.1);
    overflow: hidden;
}

.glass-pane {
    width: 100%;
    height: 100%;
    background: rgba(255, 255, 255, 0.5);
    border-radius: 16px;
    box-shadow: inset 0 0 20px rgba(255, 255, 255, 0.5);
    border: 1px solid rgba(255, 255, 255, 0.4);
    padding: 2rem;
    overflow-y: auto;
}

.visualization-container {
    display: flex;
    flex-direction: column;
    gap: 2rem;
}

/* ===== Sections ===== */
.section {
    width: 100%;
    max-width: 1000px;
    margin: 0 auto;
}

.section-title {
    font-family: var(--font-title);
    font-size: 1.5rem;
    color: var(--accent-red);
    margin-bottom: 1rem;
    text-align: center;
    letter-spacing: 0.05em;
}

/* ===== Formula Display ===== */
.formula-display-box {
    background: linear-gradient(135deg, rgba(214, 59, 29, 0.05) 0%, rgba(255, 180, 0, 0.05) 100%);
    padding: 2rem;
    border-radius: 16px;
    border: 2px solid var(--accent-red);
    box-shadow: var(--shadow-md);
}

.formula-text {
    font-family: var(--font-mono);
    font-size: 2rem;
    color: var(--accent-red);
    text-align: center;
    margin-bottom: 1.5rem;
    font-weight: 700;
    letter-spacing: 0.05em;
}

.formula-highlight {
    background: rgba(255, 255, 255, 0.8);
    padding: 0.5rem 1.5rem;
    border-radius: 12px;
    display: inline-block;
}

.formula-desc {
    text-align: center;
}

.desc-title {
    font-size: 1.2rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 0.8rem;
}

.desc-context {
    font-size: 1rem;
    color: var(--text-secondary);
    margin-bottom: 1rem;
    line-height: 1.6;
}

.theme-tag {
    display: inline-block;
    padding: 0.4rem 1rem;
    background: var(--accent-red);
    color: #fff;
    border-radius: 20px;
    font-size: 0.9rem;
    font-weight: 600;
}

/* ===== Scope Visualization ===== */
.scope-explanation {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    font-size: 0.95rem;
}

.scope-container {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.scope-item {
    background: rgba(255, 255, 255, 0.8);
    padding: 1.5rem;
    border-radius: 12px;
    border: 1px solid rgba(139, 0, 0, 0.15);
    opacity: 0;
    transform: translateX(-30px);
    transition: all 0.4s ease;
}

.scope-item.visible {
    opacity: 1;
    transform: translateX(0);
}

.scope-header {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-bottom: 1rem;
}

.scope-quantifier {
    font-family: var(--font-mono);
    font-size: 1.8rem;
    color: var(--accent-red);
    font-weight: 700;
}

.scope-type {
    padding: 0.3rem 0.8rem;
    background: var(--accent-gold);
    color: #fff;
    border-radius: 8px;
    font-size: 0.85rem;
    font-weight: 600;
}

.scope-range {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.range-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 600;
}

.range-content {
    font-family: var(--font-mono);
    font-size: 1.1rem;
    color: var(--text-primary);
    background: rgba(214, 59, 29, 0.05);
    padding: 0.8rem;
    border-radius: 8px;
    border-left: 4px solid var(--accent-red);
}

.scope-visual {
    margin-top: 1rem;
    height: 8px;
    background: rgba(139, 0, 0, 0.1);
    border-radius: 4px;
    overflow: hidden;
}

.scope-bar {
    height: 100%;
    background: linear-gradient(90deg, var(--accent-red), var(--accent-gold));
    border-radius: 4px;
    animation: scopeGrow 1s ease forwards;
}

@keyframes scopeGrow {
    from { width: 0%; }
    to { width: 100%; }
}

/* ===== Variable Analysis ===== */
.variable-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.variable-category {
    background: rgba(255, 255, 255, 0.7);
    padding: 1.5rem;
    border-radius: 12px;
    border: 1px solid rgba(139, 0, 0, 0.15);
}

.category-title {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 1.2rem;
    color: var(--accent-red);
    margin-bottom: 0.5rem;
}

.category-title .icon {
    font-size: 1.5rem;
}

.category-desc {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: 1rem;
    line-height: 1.5;
}

.variable-list {
    display: flex;
    flex-wrap: wrap;
    gap: 0.8rem;
    min-height: 60px;
}

.variable-item {
    display: flex;
    align-items: center;
    gap: 0.5rem;
    padding: 0.6rem 1rem;
    border-radius: 10px;
    opacity: 0;
    transform: scale(0.8);
    transition: all 0.3s ease;
}

.variable-item.visible {
    opacity: 1;
    transform: scale(1);
}

.variable-item.bound {
    background: var(--accent-red);
    color: #fff;
}

.variable-item.free {
    background: var(--accent-gold);
    color: #fff;
}

.var-symbol {
    font-family: var(--font-mono);
    font-size: 1.2rem;
    font-weight: 700;
}

.var-info {
    font-size: 0.8rem;
    opacity: 0.9;
}

.no-vars {
    color: var(--text-secondary);
    font-style: italic;
    font-size: 0.9rem;
}

/* ===== Closed Form Check ===== */
.closed-check-result {
    display: flex;
    justify-content: center;
}

.closed-result {
    display: flex;
    gap: 1.5rem;
    padding: 2rem;
    border-radius: 12px;
    max-width: 600px;
    opacity: 0;
    transform: scale(0.9);
    transition: all 0.4s ease;
}

.closed-result.visible {
    opacity: 1;
    transform: scale(1);
}

.closed-result.is-closed {
    background: rgba(39, 201, 63, 0.1);
    border: 2px solid var(--success-green);
}

.closed-result.not-closed {
    background: rgba(255, 180, 0, 0.1);
    border: 2px solid var(--accent-gold);
}

.result-icon {
    font-size: 3rem;
    font-weight: 700;
}

.is-closed .result-icon {
    color: var(--success-green);
}

.not-closed .result-icon {
    color: var(--accent-gold);
}

.result-content {
    flex: 1;
}

.result-title {
    font-size: 1.3rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

.is-closed .result-title {
    color: var(--success-green);
}

.not-closed .result-title {
    color: var(--accent-gold);
}

.result-desc {
    font-size: 1rem;
    color: var(--text-primary);
    margin-bottom: 0.8rem;
}

.result-explanation {
    font-size: 0.9rem;
    color: var(--text-secondary);
    font-style: italic;
    line-height: 1.6;
}

/* ===== Rename Demo ===== */
.rename-explanation {
    text-align: center;
    color: var(--text-secondary);
    margin-bottom: 1.5rem;
    font-size: 0.95rem;
    line-height: 1.6;
}

.rename-container {
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

.rename-item {
    background: rgba(255, 255, 255, 0.8);
    padding: 1.5rem;
    border-radius: 12px;
    border: 1px solid rgba(139, 0, 0, 0.15);
    opacity: 0;
    transform: translateY(20px);
    transition: all 0.4s ease;
}

.rename-item.visible {
    opacity: 1;
    transform: translateY(0);
}

.rename-header {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1rem;
    margin-bottom: 1.5rem;
}

.rename-old, .rename-new {
    font-family: var(--font-mono);
    font-size: 1.8rem;
    font-weight: 700;
    padding: 0.5rem 1rem;
    border-radius: 10px;
}

.rename-old {
    background: rgba(214, 59, 29, 0.1);
    color: var(--accent-red);
}

.rename-new {
    background: rgba(255, 180, 0, 0.1);
    color: var(--accent-gold);
}

.rename-arrow {
    font-size: 2rem;
    color: var(--text-secondary);
}

.rename-formulas {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.rename-original, .rename-result {
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.rename-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    font-weight: 600;
}

.rename-formula {
    font-family: var(--font-mono);
    font-size: 1.1rem;
    padding: 0.8rem;
    background: rgba(255, 255, 255, 0.9);
    border-radius: 8px;
    border-left: 4px solid var(--accent-red);
}

.rename-note {
    margin-top: 1rem;
    padding: 0.6rem 1rem;
    border-radius: 8px;
    font-size: 0.9rem;
}

.rename-note.success {
    background: rgba(39, 201, 63, 0.1);
    color: var(--success-green);
    border: 1px solid var(--success-green);
}

.rename-note.error {
    background: rgba(255, 59, 48, 0.1);
    color: var(--danger-red);
    border: 1px solid var(--danger-red);
}

/* ===== Tree Section ===== */
#treeSvg {
    background: rgba(255, 255, 255, 0.6);
    border-radius: 12px;
    border: 1px solid rgba(139, 0, 0, 0.15);
}

/* ===== Utility ===== */
.no-data {
    text-align: center;
    color: var(--text-secondary);
    font-style: italic;
    padding: 2rem;
}

/* ===== Scrollbar ===== */
::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: rgba(139, 0, 0, 0.05);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb {
    background: var(--accent-red);
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: var(--accent-hover);
}

/* ===== Responsive ===== */
@media (max-width: 1200px) {
    .app-container {
        flex-direction: column;
        height: 95vh;
    }

    .sidebar {
        width: 100%;
        max-height: 40vh;
        border-right: none;
        border-bottom: 1px solid var(--glass-border);
    }

    .visualizer-stage {
        padding: 1rem;
    }

    .variable-container {
        grid-template-columns: 1fr;
    }
}