:root {
    --bg: #f6f7f9;
    --panel: #ffffff;
    --text: #23262d;
    --muted: #70757f;
    --border: #d9dce2;
    --edge: #b9bec7;
    --add: #d9534f;
    --mul: #3d7dd8;
    --leaf-fill: #ffffff;
    --leaf-stroke: #9aa0aa;
    --equals-fill: #ffffff;
    --equals-stroke: #2c2f36;
    --ring: #8a8f98;
    --chip-bg: #eceef2;
}

@media (prefers-color-scheme: dark) {
    :root {
        --bg: #16181d;
        --panel: #1f2229;
        --text: #e8eaee;
        --muted: #9aa0aa;
        --border: #363b45;
        --edge: #565c68;
        --add: #e06663;
        --mul: #5b93e4;
        --leaf-fill: #262a32;
        --leaf-stroke: #7c828e;
        --equals-fill: #262a32;
        --equals-stroke: #e8eaee;
        --ring: #9aa0aa;
        --chip-bg: #2a2e37;
    }
}

* { box-sizing: border-box; }

html, body {
    height: 100%;
    margin: 0;
}

body {
    display: flex;
    flex-direction: column;
    font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
    background: var(--bg);
    color: var(--text);
}

header, footer {
    background: var(--panel);
    padding: 10px 16px;
    border-bottom: 1px solid var(--border);
}

footer {
    border-bottom: none;
    border-top: 1px solid var(--border);
}

.title-row {
    display: flex;
    align-items: baseline;
    gap: 12px;
    margin-bottom: 8px;
}

h1 {
    margin: 0;
    font-size: 20px;
}

.subtitle {
    color: var(--muted);
    font-size: 13px;
}

#input-equation, #output-equation {
    width: 100%;
    font-size: 18px;
    font-family: ui-monospace, "Cascadia Mono", Consolas, monospace;
    padding: 8px 12px;
    border: 1px solid var(--border);
    border-radius: 8px;
    background: var(--bg);
    color: var(--text);
}

#input-equation:focus {
    outline: 2px solid var(--mul);
    border-color: transparent;
}

.examples {
    display: flex;
    flex-wrap: wrap;
    gap: 6px;
    margin-top: 8px;
}

.example-chip {
    font-family: ui-monospace, "Cascadia Mono", Consolas, monospace;
    font-size: 13px;
    padding: 3px 10px;
    border: 1px solid var(--border);
    border-radius: 999px;
    background: var(--chip-bg);
    color: var(--text);
    cursor: pointer;
}

.example-chip:hover { border-color: var(--mul); }

.message {
    margin-top: 8px;
    font-size: 14px;
    padding: 4px 2px;
}

.message.hint { color: var(--muted); }
.message.warn { color: var(--add); }

main {
    flex: 1;
    min-height: 0;
    display: flex;
    position: relative;
}

#canvas {
    display: block;
    width: 100%;
    height: 100%;
    touch-action: none;
    user-select: none;
    -webkit-user-select: none;
}

.floating-controls {
    position: absolute;
    right: 12px;
    bottom: 12px;
    display: flex;
    flex-direction: column;
    align-items: stretch;
    gap: 6px;
}


.output-label {
    display: block;
    font-size: 14px;
    color: var(--muted);
    margin-bottom: 5px;
}

.output-row {
    display: flex;
    align-items: center;
    gap: 10px;
}

.output-row button,
.floating-controls button {
    font-size: 14px;
    padding: 8px 14px;
    border: 1px solid var(--border);
    border-radius: 8px;
    background: var(--chip-bg);
    color: var(--text);
    cursor: pointer;
    white-space: nowrap;
}

.output-row button:hover,
.floating-controls button:hover { border-color: var(--mul); }

.help {
    margin-top: 8px;
    font-size: 13px;
    color: var(--muted);
}

.help summary { cursor: pointer; }

.help ul {
    margin: 6px 0 0;
    padding-left: 20px;
}

.help li { margin: 3px 0; }

.swatch {
    display: inline-block;
    width: 17px;
    height: 17px;
    line-height: 17px;
    text-align: center;
    border-radius: 50%;
    color: #fff;
    font-weight: 700;
    font-size: 12px;
}

.swatch.add { background: var(--add); }
.swatch.mul { background: var(--mul); }
.legend-add { color: var(--add); font-weight: 700; }
.legend-mul { color: var(--mul); font-weight: 700; }

/* ---------------- SVG tree ---------------- */

.edge {
    stroke: var(--edge);
    stroke-width: 2;
}

.node-circle {
    stroke-width: 2;
}

.node.add .node-circle { fill: var(--add); stroke: var(--add); }
.node.mul .node-circle { fill: var(--mul); stroke: var(--mul); }
.node.leaf .node-circle { fill: var(--leaf-fill); stroke: var(--leaf-stroke); }

.node-label {
    font-family: ui-monospace, "Cascadia Mono", Consolas, monospace;
    fill: var(--text);
    pointer-events: none;
}

.node.add .node-label, .node.mul .node-label {
    fill: #fff;
    font-weight: 700;
}

.slash { cursor: pointer; }

.slash-halo {
    stroke: var(--panel);
    stroke-width: 8;
    stroke-linecap: round;
}

.slash-stroke {
    stroke-width: 4;
    stroke-linecap: round;
}

.slash-stroke.add { stroke: var(--add); }
.slash-stroke.mul { stroke: var(--mul); }

.slash-stroke.selected { stroke-width: 5.5; }

.slash-selected-ring {
    fill: none;
    stroke-width: 2;
}

.slash-selected-ring.add { stroke: var(--add); }
.slash-selected-ring.mul { stroke: var(--mul); }

.hit {
    fill: transparent;
    stroke: none;
}

.no-pointer { pointer-events: none; }

.equals { cursor: pointer; }

.equals-circle {
    fill: var(--equals-fill);
    stroke: var(--equals-stroke);
    stroke-width: 2.5;
}

.equals-select-ring {
    fill: none;
    stroke: #fff;
    stroke-width: 4;
}

.equals-label {
    font-size: 22px;
    font-weight: 700;
    fill: var(--text);
    pointer-events: none;
}

.spot circle {
    fill: var(--panel);
    fill-opacity: 0.85;
    stroke: var(--ring);
    stroke-width: 1.5;
    stroke-dasharray: 4 3;
}

.spot.dimmed { opacity: 0.25; }

.blocked-spot { fill: transparent; }

.trail-line {
    stroke: #fff;
    stroke-width: 2.5;
    stroke-dasharray: 6 5;
    stroke-linecap: round;
    opacity: 0.95;
}

.trail-line.side {
    stroke-width: 2;
    stroke-dasharray: 4 5;
    opacity: 0.8;
}

.trail-line.side.add { stroke: var(--add); }
.trail-line.side.mul { stroke: var(--mul); }

.previewing .slash { cursor: default; }
.previewing .slash.placeable { cursor: pointer; }

.slash-stroke.appearing { stroke-width: 6; }

#output-equation.previewing { opacity: 0.6; font-style: italic; }