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

:root {
    --bg: #0e0e10;
    --fg: #d4cfc4;
    --fg-dim: #7a756c;
    --accent: #c9a84c;
    --stroke: #b8a88a;
    --panel-bg: rgba(14, 14, 16, 0.94);
    --fade-duration: 0.6s;
    --header-h: 3.5rem;
}

html, body {
    height: 100%;
    overflow: hidden;
    background: var(--bg);
    color: var(--fg);
    font-family: "Palatino Linotype", Palatino, "Book Antiqua", Georgia, serif;
}

body {
    display: flex;
    flex-direction: column;
}

/* ── Header ── */
#header {
    position: fixed;
    top: 0; left: 0; right: 0;
    z-index: 30;
    display: grid;
    grid-template-columns: auto 1fr auto;
    align-items: center;
    gap: 1rem;
    padding: 0.75rem 1.25rem;
    min-height: var(--header-h);
    background: linear-gradient(to bottom, var(--panel-bg) 70%, transparent);
    opacity: 0;
    transition: opacity var(--fade-duration);
    pointer-events: none;
}

body.ui-visible #header,
body.ui-visible .controls,
body.ui-visible .side-panel:not([hidden]) {
    opacity: 1;
    pointer-events: auto;
}

#title {
    font-size: clamp(1rem, 3vw, 1.35rem);
    font-weight: 400;
    letter-spacing: 0.1em;
    color: var(--accent);
    white-space: nowrap;
}

.book-label {
    font-size: clamp(0.75rem, 2vw, 0.9rem);
    color: var(--fg-dim);
    letter-spacing: 0.04em;
    text-align: center;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

.header-nav {
    display: flex;
    align-items: center;
    gap: 0.4rem;
    flex-shrink: 0;
}

.header-btn {
    padding: 0.35rem 0.7rem;
    border: 1px solid #333;
    border-radius: 3px;
    background: var(--panel-bg);
    color: var(--fg-dim);
    font-family: inherit;
    font-size: 0.78rem;
    letter-spacing: 0.05em;
    cursor: pointer;
    transition: color 0.2s, border-color 0.2s;
    white-space: nowrap;
    list-style: none;
    user-select: none;
}

.header-btn:hover,
.header-btn:focus-visible {
    color: var(--accent);
    border-color: var(--accent);
    outline: none;
}

.book-count {
    color: var(--accent);
    margin-left: 0.2rem;
}

/* How to Use dropdown */
.how-to-use {
    position: relative;
}

.how-to-use summary::-webkit-details-marker { display: none; }

.how-to-use summary::after {
    content: " ▾";
    font-size: 0.65rem;
}

.how-to-use[open] summary::after { content: " ▴"; }

.how-to-content {
    position: absolute;
    right: 0;
    top: calc(100% + 0.4rem);
    width: min(22rem, 90vw);
    padding: 1rem 1.2rem;
    background: var(--panel-bg);
    border: 1px solid #2a2a2e;
    border-radius: 4px;
    font-size: 0.82rem;
    line-height: 1.55;
    color: var(--fg-dim);
    z-index: 40;
}

.how-to-content p { margin-bottom: 0.6rem; }
.how-to-content ul { padding-left: 1.2rem; }
.how-to-content li { margin-bottom: 0.3rem; }
.how-to-content strong { color: var(--fg); font-weight: 400; }

/* ── Side panels (Browse & Books) ── */
.side-panel {
    position: fixed;
    top: var(--header-h);
    z-index: 25;
    width: min(22rem, 92vw);
    max-height: calc(100vh - var(--header-h) - 12rem);
    background: var(--panel-bg);
    border: 1px solid #2a2a2e;
    border-radius: 4px;
    display: flex;
    flex-direction: column;
    opacity: 0;
    transition: opacity var(--fade-duration);
    pointer-events: none;
    overflow: hidden;
}

.side-panel:not([hidden]) {
    opacity: 1;
    pointer-events: auto;
}

.browse-panel { left: 1rem; }
.book-panel { right: 1rem; }

.panel-header {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.7rem 0.9rem;
    border-bottom: 1px solid #2a2a2e;
    font-size: 0.78rem;
    color: var(--fg-dim);
    letter-spacing: 0.05em;
    flex-shrink: 0;
}

.panel-header-actions {
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.panel-close {
    background: none;
    border: none;
    color: var(--fg-dim);
    font-size: 1.2rem;
    line-height: 1;
    cursor: pointer;
    padding: 0 0.2rem;
}

.panel-close:hover { color: var(--accent); }

.link-btn {
    background: none;
    border: none;
    color: var(--accent);
    font-family: inherit;
    font-size: 0.72rem;
    cursor: pointer;
    text-decoration: underline;
    text-underline-offset: 2px;
}

/* Browse list */
.browse-list {
    overflow-y: auto;
    flex: 1;
    padding: 0.5rem 0;
}

.browse-book { border-bottom: 1px solid #1e1e22; }

.browse-book summary {
    padding: 0.55rem 0.9rem;
    font-size: 0.82rem;
    color: var(--fg);
    cursor: pointer;
    list-style: none;
    display: flex;
    align-items: baseline;
    gap: 0.5rem;
}

.browse-book summary::-webkit-details-marker { display: none; }

.browse-book summary::before {
    content: "▸";
    font-size: 0.7rem;
    color: var(--accent);
    transition: transform 0.15s;
}

.browse-book[open] summary::before { transform: rotate(90deg); }

.browse-book-num {
    color: var(--accent);
    font-weight: 400;
    min-width: 1.5rem;
}

.browse-book-title {
    color: var(--fg-dim);
    font-size: 0.75rem;
}

.browse-entries { padding: 0.2rem 0 0.5rem; }

.browse-entry {
    display: block;
    width: 100%;
    text-align: left;
    padding: 0.55rem 1rem 0.55rem 2rem;
    border: none;
    background: none;
    color: var(--fg-dim);
    font-family: inherit;
    font-size: 0.88rem;
    line-height: 1.45;
    cursor: pointer;
    transition: background 0.15s, color 0.15s;
}

.browse-entry:hover {
    background: rgba(201, 168, 76, 0.08);
    color: var(--fg);
}

.browse-entry.active {
    background: rgba(201, 168, 76, 0.15);
    color: var(--accent);
    border-left: 2px solid var(--accent);
    padding-left: calc(2rem - 2px);
}

.browse-entry-id {
    display: block;
    font-size: 0.72rem;
    color: var(--accent);
    margin-bottom: 0.15rem;
    letter-spacing: 0.04em;
}

.browse-entry.disabled { opacity: 0.45; }

/* Book checkboxes */
.book-checkboxes {
    overflow-y: auto;
    flex: 1;
    padding: 0.6rem 0.9rem;
    display: flex;
    flex-direction: column;
    gap: 0.25rem;
}

.book-checkboxes label {
    display: flex;
    align-items: flex-start;
    gap: 0.5rem;
    font-size: 0.78rem;
    color: var(--fg-dim);
    cursor: pointer;
    padding: 0.15rem 0;
    line-height: 1.3;
}

.book-checkboxes label:hover { color: var(--fg); }

.book-checkboxes input[type="checkbox"] {
    accent-color: var(--accent);
    margin-top: 0.15rem;
    flex-shrink: 0;
}

.book-checkboxes .book-num {
    color: var(--accent);
    min-width: 1.2rem;
}

/* ── Stage (SVG visualizer) ── */
#stage {
    flex: 1 1 auto;
    min-height: 0;
    margin-top: var(--header-h);
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 1.25rem 2rem 0.75rem;
    overflow: hidden;
}

#canvas {
    width: 100%;
    height: 100%;
    max-width: 780px;
    max-height: 100%;
    color: var(--stroke);
}

#drawing-layer line,
#drawing-layer circle,
#drawing-layer polygon,
#drawing-layer path,
#drawing-layer rect,
#drawing-layer ellipse {
    fill: none;
    stroke: var(--stroke);
    stroke-linecap: round;
    stroke-linejoin: round;
}

#drawing-layer .point {
    fill: var(--accent);
    stroke: none;
}

#drawing-layer .label {
    fill: var(--fg-dim);
    stroke: none;
    font-family: inherit;
    font-size: 14px;
    font-style: italic;
}

#drawing-layer .highlight {
    stroke: var(--accent);
    stroke-width: 2.5;
}

.anim-draw {
    stroke-dasharray: var(--dash-len);
    stroke-dashoffset: var(--dash-len);
    animation: draw-stroke 0.9s ease forwards;
}

.anim-fade {
    opacity: 0;
    animation: fade-in 0.5s ease forwards;
}

@keyframes draw-stroke {
    to { stroke-dashoffset: 0; }
}

@keyframes fade-in {
    to { opacity: 1; }
}

/* ── Footer (controls + text) ── */
#footer {
    flex-shrink: 0;
    z-index: 10;
    padding: 0.5rem 2rem 1.5rem;
    background: linear-gradient(to top, var(--panel-bg) 85%, transparent);
    text-align: center;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.85rem;
}

.content-text {
    font-size: clamp(1.15rem, 3.2vw, 1.65rem);
    line-height: 1.6;
    max-width: 48rem;
    margin: 0 auto;
    color: var(--fg);
}

.step-indicator {
    font-size: clamp(0.8rem, 2vw, 0.95rem);
    color: var(--fg-dim);
    letter-spacing: 0.06em;
}

/* ── Navigation controls ── */
.controls {
    display: flex;
    gap: 0.65rem;
    opacity: 0;
    transition: opacity var(--fade-duration);
    pointer-events: none;
}

.ctrl-btn {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    gap: 0.2rem;
    width: clamp(2.8rem, 9vw, 3.4rem);
    height: clamp(3.2rem, 10vw, 3.8rem);
    border: 1px solid #333;
    border-radius: 8px;
    background: var(--panel-bg);
    color: var(--fg-dim);
    cursor: pointer;
    transition: color 0.2s, border-color 0.2s, background 0.2s, box-shadow 0.2s;
    padding: 0.3rem 0.2rem 0.25rem;
}

.ctrl-icon {
    font-size: 1rem;
    line-height: 1;
}

.ctrl-key {
    font-family: inherit;
    font-size: 0.58rem;
    letter-spacing: 0.03em;
    color: var(--fg-dim);
    background: rgba(255, 255, 255, 0.05);
    border: 1px solid #333;
    border-radius: 3px;
    padding: 0.1rem 0.3rem;
    line-height: 1.3;
}

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

.ctrl-btn:hover .ctrl-key {
    color: var(--accent);
    border-color: var(--accent);
}

.ctrl-btn.active {
    color: var(--bg);
    background: var(--accent);
    border-color: var(--accent);
    box-shadow: 0 0 12px rgba(201, 168, 76, 0.45);
}

.ctrl-btn.active .ctrl-key {
    color: var(--bg);
    background: rgba(0, 0, 0, 0.2);
    border-color: rgba(0, 0, 0, 0.25);
}

#play-pause .ctrl-icon { font-size: 0.85rem; }

/* ── Responsive ── */
@media (max-width: 720px) {
    :root { --header-h: auto; }

    #header {
        grid-template-columns: 1fr;
        grid-template-rows: auto auto auto;
        gap: 0.4rem;
        padding: 0.6rem 1rem;
    }

    .book-label { text-align: left; }

    .header-nav {
        flex-wrap: wrap;
        justify-content: flex-start;
    }

    .how-to-content {
        left: 0;
        right: auto;
    }

    .browse-panel,
    .book-panel {
        left: 0.5rem;
        right: 0.5rem;
        width: auto;
        max-height: 40vh;
    }

    #stage {
        margin-top: 5.5rem;
        padding: 0.75rem 1rem 0.5rem;
    }

    #footer {
        padding: 0.5rem 1rem 1rem;
        gap: 0.65rem;
    }

    .ctrl-key { font-size: 0.52rem; }
}

@media (max-width: 400px) {
    .header-nav { gap: 0.3rem; }

    .header-btn {
        font-size: 0.72rem;
        padding: 0.3rem 0.5rem;
    }

    .ctrl-btn {
        width: 2.6rem;
        height: 3rem;
    }
}

@media (min-width: 721px) {
    body.browse-open #stage,
    body.book-open #stage {
        transition: padding 0.3s;
    }

    body.browse-open #stage {
        padding-left: min(23rem, 38vw);
    }

    body.book-open #stage {
        padding-right: min(23rem, 38vw);
    }
}