:root {
    /* Rhythm Red & Stability Blue Theme */
    --app-bg: #fdfbf7;
    --panel-bg: rgba(255, 255, 255, 0.9);
    --glass-border: rgba(0, 0, 0, 0.08);
    --text-primary: #2d3436;
    --text-secondary: #636e72;

    --rhythm-red: #d63031;
    --stability-blue: #0984e3;
    --growth-green: #00b894;
    --constant-gold: #fdcb6e;

    --shadow-sm: 0 4px 6px rgba(0, 0, 0, 0.05);
    --shadow-md: 0 10px 20px rgba(0, 0, 0, 0.08);

    --font-family: "Noto Serif SC", "Outfit", serif;
    --font-mono: "JetBrains Mono", monospace;
    --font-title: "Ma Shan Zheng", cursive;
}

* {
    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-1516961642265-531546e84af2?q=80&w=2574&auto=format&fit=crop');
    background-size: cover;
    background-position: center;
}

.app-container {
    width: 95vw;
    height: 90vh;
    max-width: 1600px;
    background: rgba(255, 252, 245, 0.96);
    backdrop-filter: blur(20px);
    border-radius: 24px;
    border: 1px solid var(--glass-border);
    box-shadow: var(--shadow-md);
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

/* Header */
.main-header {
    padding: 1.2rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--glass-border);
    background: rgba(255, 255, 255, 0.6);
}

.header-content h1 {
    font-family: var(--font-title);
    font-size: 2rem;
    font-weight: 400;
    color: var(--rhythm-red);
}

.highlight {
    color: var(--stability-blue);
}

.subtitle {
    font-size: 0.9rem;
    color: var(--text-secondary);
    font-style: italic;
    margin-top: -5px;
}

.header-controls {
    display: flex;
    gap: 16px;
    align-items: center;
}

.mode-nav {
    display: flex;
    background: #fff;
    padding: 4px;
    border-radius: 12px;
    border: 1px solid rgba(0, 0, 0, 0.08);
}

.nav-btn {
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 8px 16px;
    border: none;
    background: transparent;
    border-radius: 8px;
    cursor: pointer;
    transition: all 0.3s ease;
    opacity: 0.7;
    font-family: var(--font-family);
    font-weight: 600;
}

.nav-btn:hover {
    opacity: 1;
    background: rgba(0, 0, 0, 0.02);
}

.nav-btn.active {
    opacity: 1;
    background: var(--rhythm-red);
    color: white;
    box-shadow: 0 2px 8px rgba(214, 48, 49, 0.3);
}

.nav-btn[data-mode="monotonic"].active {
    background: var(--growth-green);
    box-shadow: 0 2px 8px rgba(0, 184, 148, 0.3);
}

.nav-btn[data-mode="constant"].active {
    background: var(--constant-gold);
    box-shadow: 0 2px 8px rgba(253, 203, 110, 0.3);
}

.nav-btn[data-mode="periodic"].active {
    background: var(--stability-blue);
    box-shadow: 0 2px 8px rgba(9, 132, 227, 0.3);
}

.apple-btn {
    padding: 10px;
    border-radius: 10px;
    border: 1px solid rgba(0, 0, 0, 0.1);
    background: #fff;
    cursor: pointer;
    transition: all 0.2s;
    color: var(--text-secondary);
}

.apple-btn:hover {
    background: #f5f5f5;
    transform: scale(1.05);
}

/* Main Stage */
.main-stage {
    flex-grow: 1;
    display: grid;
    grid-template-columns: 1fr 350px;
    gap: 2px;
    background: rgba(0, 0, 0, 0.02);
    overflow: hidden;
}

.graph-panel,
.insight-panel {
    background: var(--panel-bg);
    display: flex;
    flex-direction: column;
    overflow: hidden;
    position: relative;
}

.canvas-container {
    flex-grow: 1;
    position: relative;
    background: #fff;
    cursor: crosshair;
}

#functionCanvas {
    width: 100%;
    height: 100%;
}

.overlay-text {
    position: absolute;
    top: 20px;
    left: 20px;
    font-size: 1.2rem;
    font-weight: 600;
    color: var(--text-primary);
    pointer-events: none;
    background: rgba(255, 255, 255, 0.8);
    padding: 8px 12px;
    border-radius: 8px;
    opacity: 0;
    transition: opacity 0.3s;
}

.controls-bar {
    padding: 20px;
    background: #fff;
    border-top: 1px solid var(--glass-border);
    display: flex;
    gap: 24px;
    align-items: center;
    justify-content: center;
    min-height: 80px;
}

.control-group {
    display: flex;
    flex-direction: column;
    gap: 8px;
    min-width: 200px;
}

.control-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    display: flex;
    justify-content: space-between;
}

input[type="range"] {
    width: 100%;
    accent-color: var(--rhythm-red);
}

/* Insight Panel */
.insight-panel {
    padding: 24px;
    gap: 20px;
    border-left: 1px solid var(--glass-border);
}

.concept-card,
.insight-card,
.stats-box {
    background: #fff;
    border-radius: 16px;
    padding: 20px;
    box-shadow: var(--shadow-sm);
    border: 1px solid rgba(0, 0, 0, 0.05);
}

.concept-card {
    border-top: 4px solid var(--rhythm-red);
}

.card-header {
    display: flex;
    align-items: center;
    gap: 12px;
    margin-bottom: 12px;
}

.card-icon {
    font-size: 1.6rem;
}

.card-header h4 {
    font-size: 1.1rem;
    color: var(--text-primary);
}

.card-desc {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.6;
    margin-bottom: 16px;
}

.math-box {
    background: rgba(0, 0, 0, 0.03);
    padding: 12px;
    border-radius: 8px;
    font-family: var(--font-mono);
    font-size: 1rem;
    color: var(--text-primary);
    text-align: center;
    border: 1px dashed rgba(0, 0, 0, 0.2);
}

/* Insight */
.insight-card {
    background: linear-gradient(135deg, #fff5f5 0%, #fff 100%);
    border: 1px solid rgba(214, 48, 49, 0.2);
}

.insight-card h4 {
    color: var(--rhythm-red);
    margin-bottom: 10px;
    font-size: 1rem;
}

.insight-card p {
    font-size: 0.9rem;
    color: var(--text-secondary);
    line-height: 1.6;
}

/* Stats */
.stats-box {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
}

.stat-item {
    display: flex;
    flex-direction: column;
    align-items: center;
}

.stat-label {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-bottom: 4px;
}

.stat-value {
    font-size: 1.4rem;
    font-weight: 700;
    color: var(--text-primary);
    font-family: var(--font-mono);
}