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

:root {
    --bg: #0a0a0f;
    --bg-card: #12121a;
    --bg-control: #16161f;
    --text: #c8c8d0;
    --text-dim: #7a7a8e;
    --accent: #5b8def;
    --accent-dim: #3a5a9e;
    --border: #1e1e2e;
    --red: #e05555;
}

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

body {
    background: var(--bg);
    color: var(--text);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    line-height: 1.6;
    min-height: 100vh;
}

/* --- header --- */

header {
    text-align: center;
    padding: 3rem 1.5rem 1.5rem;
}

header h1 {
    font-size: 2.4rem;
    font-weight: 700;
    letter-spacing: 0.04em;
    color: #eee;
}

.subtitle {
    font-size: 1rem;
    color: var(--accent);
    margin-top: 0.3rem;
}

.tagline {
    font-size: 0.88rem;
    color: var(--text-dim);
    margin-top: 0.2rem;
}

/* --- layout --- */

main {
    max-width: 780px;
    margin: 0 auto;
    padding: 0 1.5rem 4rem;
}

/* --- canvas --- */

.canvas-section {
    text-align: center;
    margin-bottom: 1.2rem;
}

#heatmap {
    display: block;
    margin: 0 auto;
    border: 1px solid var(--border);
    border-radius: 6px;
    cursor: grab;
    max-width: 100%;
    height: auto;
    background: #050508;
}

#heatmap:active {
    cursor: grabbing;
}

.canvas-hint {
    font-size: 0.78rem;
    color: var(--text-dim);
    margin-top: 0.5rem;
}

/* --- controls --- */

.controls {
    display: flex;
    gap: 1.5rem;
    margin-bottom: 1.4rem;
    flex-wrap: wrap;
}

.control-group {
    flex: 1;
    min-width: 200px;
    background: var(--bg-control);
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 0.9rem 1.1rem;
}

.control-group label {
    display: block;
    font-size: 0.82rem;
    color: var(--text-dim);
    margin-bottom: 0.4rem;
}

.control-group label em {
    font-style: italic;
}

.control-group input[type="range"] {
    width: calc(100% - 3rem);
    vertical-align: middle;
    accent-color: var(--accent);
}

.slider-val {
    display: inline-block;
    width: 2.5rem;
    text-align: right;
    font-size: 0.9rem;
    font-variant-numeric: tabular-nums;
    color: #ddd;
}

/* --- info panel --- */

.info-panel {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 0.8rem;
    margin-bottom: 2.2rem;
}

.info-card {
    background: var(--bg-card);
    border: 1px solid var(--border);
    border-radius: 6px;
    padding: 0.8rem 1rem;
    text-align: center;
}

.info-label {
    display: block;
    font-size: 0.75rem;
    color: var(--text-dim);
    margin-bottom: 0.25rem;
}

.info-value {
    display: block;
    font-size: 1.15rem;
    font-weight: 600;
    color: #eee;
    font-variant-numeric: tabular-nums;
}

/* --- explainer --- */

.explainer {
    border-top: 1px solid var(--border);
    padding-top: 2rem;
}

.explainer h2 {
    font-size: 1.1rem;
    font-weight: 600;
    color: #ddd;
    margin-bottom: 0.6rem;
}

.explainer h2:not(:first-child) {
    margin-top: 1.6rem;
}

.explainer p {
    margin-bottom: 0.7rem;
    font-size: 0.92rem;
    color: var(--text);
}

.formula {
    font-family: "Times New Roman", "Georgia", serif;
    font-size: 1.05rem;
    text-align: center;
    padding: 0.6rem 0;
    color: #ddd;
}

.repo-link {
    color: var(--accent);
    text-decoration: none;
    border-bottom: 1px solid var(--accent-dim);
    transition: border-color 0.2s;
}

.repo-link:hover {
    border-color: var(--accent);
}

/* --- footer --- */

footer {
    text-align: center;
    padding: 2rem 1rem;
    font-size: 0.78rem;
    color: var(--text-dim);
    border-top: 1px solid var(--border);
}

/* --- mobile --- */

@media (max-width: 600px) {
    header {
        padding: 2rem 1rem 1rem;
    }

    header h1 {
        font-size: 1.8rem;
    }

    main {
        padding: 0 1rem 3rem;
    }

    .controls {
        flex-direction: column;
        gap: 0.8rem;
    }

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