/* ==============================
   Design System & Variables
   ============================== */
:root {
    --bg-primary: #0a0e1a;
    --bg-secondary: #111827;
    --bg-panel: #141b2d;
    --bg-card: #1a2238;
    --bg-hover: #1e2a45;

    --text-primary: #e8ecf4;
    --text-secondary: #8b95a8;
    --text-muted: #5a6478;

    --accent-blue: #3b82f6;
    --accent-cyan: #06b6d4;
    --accent-purple: #8b5cf6;
    --accent-green: #10b981;
    --accent-orange: #f59e0b;
    --accent-red: #ef4444;
    --accent-pink: #ec4899;

    --border-color: #1e293b;
    --border-accent: #2a3a5c;

    --glass-bg: rgba(20, 27, 45, 0.85);
    --glass-border: rgba(59, 130, 246, 0.15);

    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 20px;

    --shadow-sm: 0 2px 8px rgba(0,0,0,0.2);
    --shadow-md: 0 4px 16px rgba(0,0,0,0.3);
    --shadow-lg: 0 8px 32px rgba(0,0,0,0.4);
    --shadow-glow: 0 0 20px rgba(59, 130, 246, 0.15);

    --font-sans: 'Inter', -apple-system, sans-serif;
    --font-mono: 'JetBrains Mono', 'Fira Code', monospace;

    --transition-fast: 150ms ease;
    --transition-med: 250ms ease;
    --transition-slow: 400ms cubic-bezier(.4,0,.2,1);
}

/* ==============================
   Reset & Base
   ============================== */
*, *::before, *::after {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: var(--font-sans);
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    overflow-x: hidden;
    padding: 16px;
    padding-top: 8px;
}

/* Subtle background gradient */
body::before {
    content: '';
    position: fixed;
    top: 0; left: 0; right: 0; bottom: 0;
    background:
        radial-gradient(ellipse at 20% 20%, rgba(59, 130, 246, 0.06) 0%, transparent 50%),
        radial-gradient(ellipse at 80% 80%, rgba(139, 92, 246, 0.05) 0%, transparent 50%);
    pointer-events: none;
    z-index: 0;
}

/* ==============================
   Back Button
   ============================== */
.back-btn {
    position: fixed;
    top: 16px;
    right: 16px;
    z-index: 100;
    display: flex;
    align-items: center;
    gap: 6px;
    padding: 8px 16px;
    background: var(--glass-bg);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-md);
    color: var(--text-secondary);
    font-family: var(--font-sans);
    font-size: 0.85rem;
    font-weight: 500;
    cursor: pointer;
    backdrop-filter: blur(12px);
    transition: all var(--transition-med);
    box-shadow: var(--shadow-sm);
}

.back-btn:hover {
    color: var(--accent-blue);
    border-color: var(--accent-blue);
    box-shadow: var(--shadow-glow);
    transform: translateX(-2px);
}

/* ==============================
   Header
   ============================== */
#appHeader {
    position: relative;
    z-index: 1;
    text-align: center;
    padding: 12px 0 16px;
}

#appHeader h1 {
    font-size: 1.6rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.02em;
}

.subtitle {
    margin-top: 4px;
    font-size: 0.85rem;
    color: var(--text-secondary);
}

.pole-sym {
    color: var(--accent-cyan);
    font-weight: 700;
    font-size: 1rem;
}

.zero-sym {
    color: var(--accent-green);
    font-weight: 700;
    font-size: 1rem;
}

/* ==============================
   Main Layout
   ============================== */
#mainLayout {
    position: relative;
    z-index: 1;
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 20px;
    max-width: 1500px;
    margin: 0 auto;
}

/* ==============================
   Panel
   ============================== */
.panel {
    background: var(--bg-panel);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 20px;
    box-shadow: var(--shadow-md);
    display: flex;
    flex-direction: column;
}

.panel-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    margin-bottom: 14px;
    flex-wrap: wrap;
    gap: 8px;
}

.panel-header h2 {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-primary);
}

.legend {
    display: flex;
    gap: 14px;
    flex-wrap: wrap;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: 5px;
    font-size: 0.72rem;
    color: var(--text-secondary);
}

.legend-dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
}

.legend-dot.ol-pole {
    background: var(--accent-cyan);
    border: 2px solid var(--accent-cyan);
    background: none;
    position: relative;
}
.legend-dot.ol-pole::after {
    content: '✕';
    font-size: 8px;
    color: var(--accent-cyan);
    position: absolute;
    top: -2px; left: 0;
}

.legend-dot.ol-zero {
    background: none;
    border: 2px solid var(--accent-green);
}

.legend-dot.cl-pole {
    background: var(--accent-orange);
}

/* ==============================
   Canvas Wrapper
   ============================== */
.canvas-wrap {
    position: relative;
    width: 100%;
    border-radius: var(--radius-md);
    overflow: hidden;
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    flex: 1;
    min-height: 350px;
}

.canvas-wrap canvas {
    display: block;
    width: 100%;
    height: 100%;
}

/* ==============================
   Transfer Function Display
   ============================== */
.tf-display {
    margin-top: 12px;
    padding: 12px 16px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
}

.tf-label {
    font-size: 0.72rem;
    color: var(--text-muted);
    font-family: var(--font-mono);
    margin-bottom: 6px;
}

.tf-formula {
    font-family: var(--font-mono);
    font-size: 0.82rem;
    color: var(--accent-cyan);
    word-break: break-all;
    line-height: 1.6;
}

/* ==============================
   Stability Badge
   ============================== */
.stability-badge {
    padding: 4px 12px;
    border-radius: 20px;
    font-size: 0.72rem;
    font-weight: 600;
    letter-spacing: 0.05em;
    transition: all var(--transition-med);
}

.stability-badge.stable {
    background: rgba(16, 185, 129, 0.15);
    color: var(--accent-green);
    border: 1px solid rgba(16, 185, 129, 0.3);
}

.stability-badge.unstable {
    background: rgba(239, 68, 68, 0.15);
    color: var(--accent-red);
    border: 1px solid rgba(239, 68, 68, 0.3);
    animation: pulse-red 1.5s ease-in-out infinite;
}

@keyframes pulse-red {
    0%, 100% { box-shadow: 0 0 0 0 rgba(239, 68, 68, 0); }
    50% { box-shadow: 0 0 12px 2px rgba(239, 68, 68, 0.25); }
}

/* ==============================
   Slider
   ============================== */
.slider-container {
    margin-top: 16px;
    padding: 14px 16px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
}

.slider-container label {
    font-size: 0.8rem;
    font-weight: 600;
    color: var(--text-secondary);
    margin-bottom: 8px;
    display: block;
}

.slider-row {
    display: flex;
    align-items: center;
    gap: 14px;
}

.slider-value {
    font-family: var(--font-mono);
    font-size: 1rem;
    font-weight: 600;
    color: var(--accent-blue);
    min-width: 52px;
    text-align: right;
}

input[type="range"] {
    -webkit-appearance: none;
    appearance: none;
    flex: 1;
    height: 6px;
    background: var(--bg-hover);
    border-radius: 3px;
    outline: none;
    cursor: pointer;
}

input[type="range"]::-webkit-slider-thumb {
    -webkit-appearance: none;
    appearance: none;
    width: 22px;
    height: 22px;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
    cursor: pointer;
    box-shadow: 0 0 8px rgba(59, 130, 246, 0.4);
    transition: transform var(--transition-fast);
}

input[type="range"]::-webkit-slider-thumb:hover {
    transform: scale(1.15);
}

input[type="range"]::-moz-range-thumb {
    width: 22px;
    height: 22px;
    border: none;
    border-radius: 50%;
    background: linear-gradient(135deg, var(--accent-blue), var(--accent-purple));
    cursor: pointer;
    box-shadow: 0 0 8px rgba(59, 130, 246, 0.4);
}

/* ==============================
   Info Cards
   ============================== */
.info-cards {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
    margin-top: 12px;
}

.info-card {
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 10px 12px;
    display: flex;
    flex-direction: column;
    gap: 4px;
}

.info-label {
    font-size: 0.68rem;
    color: var(--text-muted);
    font-weight: 500;
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.info-value {
    font-family: var(--font-mono);
    font-size: 0.78rem;
    color: var(--text-primary);
    word-break: break-all;
}

/* ==============================
   Impulse Canvas Unstable BG
   ============================== */
#impulseWrap.unstable-bg {
    background: rgba(239, 68, 68, 0.08);
    border-color: rgba(239, 68, 68, 0.3);
    transition: background var(--transition-slow), border-color var(--transition-slow);
}

/* ==============================
   Touch / Drag hints
   ============================== */
.canvas-wrap.dragging {
    cursor: grabbing;
}

/* ==============================
   Responsive: Tablet
   ============================== */
@media (max-width: 1024px) {
    #mainLayout {
        grid-template-columns: 1fr 1fr;
        gap: 16px;
    }
    .canvas-wrap {
        min-height: 300px;
    }
}

/* ==============================
   Responsive: Mobile (< 768px)
   ============================== */
@media (max-width: 768px) {
    body {
        padding: 10px;
        padding-top: 6px;
    }

    #appHeader h1 {
        font-size: 1.25rem;
    }

    .subtitle {
        font-size: 0.75rem;
    }

    #mainLayout {
        grid-template-columns: 1fr;
        gap: 14px;
    }

    .panel {
        padding: 14px;
    }

    .canvas-wrap {
        min-height: 280px;
    }

    .legend {
        gap: 8px;
    }

    .info-cards {
        grid-template-columns: 1fr 1fr 1fr;
        gap: 8px;
    }

    .back-btn {
        top: 10px;
        right: 10px;
        padding: 6px 12px;
        font-size: 0.8rem;
    }

    input[type="range"]::-webkit-slider-thumb {
        width: 28px;
        height: 28px;
    }

    input[type="range"]::-moz-range-thumb {
        width: 28px;
        height: 28px;
    }
}

/* ==============================
   Responsive: Small phones (< 420px)
   ============================== */
@media (max-width: 420px) {
    #appHeader h1 {
        font-size: 1.1rem;
    }

    .info-cards {
        grid-template-columns: 1fr;
    }

    .canvas-wrap {
        min-height: 240px;
    }
}