:root {
    --bg: #0f172a;
    --panel: #111827;
    --card: #1f2937;
    --muted: #9ca3af;
    --accent: #22d3ee;
    --good: #22c55e;
    --bad: #ef4444;
    --line: #334155;
    --thick: #94a3b8;
}

* {
    box-sizing: border-box
}

body {
    margin: 0;
    font-family: system-ui, -apple-system, Segoe UI, Roboto, Ubuntu, Cantarell, Noto Sans, "Helvetica Neue", Arial, "Apple Color Emoji", "Segoe UI Emoji";
    background: radial-gradient(1200px 800px at 10% -10%, #0b132b 0%, #0f172a 60%);
    color: #e5e7eb;
    min-height: 100svh;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 16px;
}

.top {
    position: absolute;
    top: 10px;
    left: 10px;
}

.top img {
    height: 40px;
    padding: 5px;
    margin: 5px;
}

.app {
    width: 100%;
    max-width: 1100px;
    display: grid;
    grid-template-columns: 1fr 320px;
    gap: 20px;
}

@media (max-width: 900px) {
    .app {
        grid-template-columns: 1fr;
    }
}

.board-wrap {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.toolbar {
    display: flex;
    flex-wrap: wrap;
    gap: 10px;
    align-items: center;
    background: var(--panel);
    padding: 12px;
    border-radius: 16px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, .35);
}

.toolbar .group {
    display: flex;
    gap: 8px;
    align-items: center;
}

.toolbar label {
    font-size: 14px;
    color: var(--muted);
}

select,
button {
    background: var(--card);
    color: #e5e7eb;
    border: 1px solid #243244;
    padding: 10px 12px;
    border-radius: 12px;
    font: inherit;
    cursor: pointer;
}

button.primary {
    background: linear-gradient(180deg, #1fb6d8, #0ea5b3);
    border: none;
}

button.warn {
    background: #3b1f26;
    border: 1px solid #883e4a;
    color: #fecaca;
}

button:disabled {
    opacity: .6;
    cursor: not-allowed;
}

.hud {
    display: flex;
    gap: 16px;
    align-items: center;
    color: var(--muted);
    font-size: 14px;
    flex-wrap: wrap;
}

.board {
    width: 100%;
    max-width: 580px;
    aspect-ratio: 1;
    background: var(--panel);
    border-radius: 16px;
    padding: 10px;
    box-shadow: inset 0 0 0 1px #1e293b, 0 20px 50px rgba(0, 0, 0, .45);
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    grid-template-rows: repeat(9, 1fr);
    gap: 2px;
}

.cell {
    position: relative;
    background: #0b1220;
    border-radius: 8px;
    overflow: hidden;
    display: flex;
    align-items: center;
    justify-content: center;
    user-select: none;
    cursor: pointer;
    font-weight: 600;
    font-size: clamp(14px, 2vw, 28px);
    border: 1px solid var(--line);
}

.cell[data-btop] {
    border-top-color: var(--thick);
    border-top-width: 2px;
}

.cell[data-bleft] {
    border-left-color: var(--thick);
    border-left-width: 2px;
}

.cell[data-bright] {
    border-right-color: var(--thick);
    border-right-width: 2px;
}

.cell[data-bbottom] {
    border-bottom-color: var(--thick);
    border-bottom-width: 2px;
}

.cell.given {
    background: #0f1a2c;
}

.cell.selected {
    outline: 2px solid var(--accent);
    z-index: 2;
}

.cell.highlight {
    background: #0c2131;
}

.cell.conflict {
    background: #3a0f1a;
}

.note-grid {
    position: absolute;
    inset: 0;
    padding: 4px;
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    gap: 2px;
    opacity: .9;
}

.note {
    font-size: clamp(8px, 1.2vw, 13px);
    color: #93c5fd;
    display: flex;
    align-items: center;
    justify-content: center;
}

.value {
    transition: transform .08s ease;
}

.cell.pop .value {
    transform: scale(1.08);
}

.side {
    display: flex;
    flex-direction: column;
    gap: 16px;
}

.panel {
    background: var(--panel);
    border-radius: 16px;
    padding: 16px;
    box-shadow: 0 12px 30px rgba(0, 0, 0, .35);
}

.panel h3 {
    margin: 0 0 12px;
    font-size: 16px;
    color: #cbd5e1;
    font-weight: 700;
}

.numpad {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 8px;
}

.numpad button {
    padding: 18px 0;
    font-size: clamp(16px, 5vw, 20px);
    border-radius: 14px;
}

.controls {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 8px;
}

.legend {
    display: flex;
    gap: 10px;
    flex-wrap: wrap;
    font-size: 12px;
    color: var(--muted);
}

.dot {
    width: 10px;
    height: 10px;
    border-radius: 50%;
    display: inline-block;
    margin-right: 4px;
}

.dot.given {
    background: #0f1a2c;
}

.dot.sel {
    background: var(--accent);
}

.dot.hi {
    background: #0c2131;
}

.dot.con {
    background: #3a0f1a;
}

.footer {
    opacity: .7;
    font-size: 12px;
    text-align: center;
}

a {
    color: #67e8f9;
    text-decoration: none;
}

@media (max-width: 600px) {
    .toolbar {
        flex-direction: column;
        align-items: stretch;
    }
    .controls {
        grid-template-columns: 1fr;
    }
    .hud {
        justify-content: center;
    }
    .side {
        flex-direction: column;
    }
    .numpad button {
        padding: 14px 0;
    }
}