:root {
    --bg: #f6f7f9;
    --surface: #ffffff;
    --text: #1b1d21;
    --muted: #6b7280;
    --line: #d4d7dd;
    --rule: #1b1d21;
    --accent: #2f6fed;
    --given: #1b1d21;
    --entry: #2f6fed;
    --conflict-bg: #fdecec;
    --conflict-fg: #c02626;
    --wrong-bg: #fff4d6;
    --wrong-fg: #9a6200;
    --success: #157347;
    --cell: 44px;
    --radius: 10px;
    color-scheme: light dark;
}

@media (prefers-color-scheme: dark) {
    :root {
        --bg: #14161a;
        --surface: #1c1f25;
        --text: #e7e9ee;
        --muted: #9aa1ad;
        --line: #333842;
        --rule: #8a93a3;
        --accent: #6f9bff;
        --given: #e7e9ee;
        --entry: #6f9bff;
        --conflict-bg: #3b1f22;
        --conflict-fg: #ff8b8b;
        --wrong-bg: #3a2f18;
        --wrong-fg: #ffc86b;
        --success: #46c88a;
    }
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: 2rem 1rem 3rem;
    min-height: 100vh;
    background: var(--bg);
    color: var(--text);
    font-family: system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1.75rem;
}

.app-header {
    width: 100%;
    max-width: 40rem;
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1.25rem;
}

h1 {
    margin: 0;
    font-size: 1.75rem;
    font-weight: 650;
    letter-spacing: -0.02em;
}

.controls {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: center;
    gap: 0.75rem 1rem;
}

.segmented {
    display: inline-flex;
    background: var(--surface);
    border: 1px solid var(--line);
    border-radius: var(--radius);
    overflow: hidden;
}

.segmented button {
    padding: 0.5rem 0.9rem;
    border: 0;
    background: transparent;
    color: var(--muted);
    font: inherit;
    font-size: 0.9rem;
    cursor: pointer;
    transition: background 0.15s, color 0.15s;
}

.segmented button + button {
    border-left: 1px solid var(--line);
}

.segmented button:hover {
    color: var(--text);
}

.segmented button.is-active {
    background: var(--accent);
    color: #fff;
}

.field {
    display: inline-flex;
    align-items: center;
    gap: 0.5rem;
    font-size: 0.9rem;
    color: var(--muted);
}

select {
    padding: 0.5rem 0.6rem;
    border: 1px solid var(--line);
    border-radius: var(--radius);
    background: var(--surface);
    color: var(--text);
    font: inherit;
    font-size: 0.9rem;
    cursor: pointer;
}

.actions {
    display: flex;
    flex-wrap: wrap;
    gap: 0.5rem;
}

.button {
    padding: 0.5rem 0.9rem;
    border: 1px solid var(--line);
    border-radius: var(--radius);
    background: var(--surface);
    color: var(--text);
    font: inherit;
    font-size: 0.9rem;
    cursor: pointer;
    transition: border-color 0.15s, transform 0.05s;
}

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

.button:active {
    transform: translateY(1px);
}

.button--primary {
    background: var(--accent);
    border-color: var(--accent);
    color: #fff;
}

:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 2px;
}

/* The board is a plain grid; --size is set per board size from JS. */
.board {
    display: grid;
    grid-template-columns: repeat(var(--size, 9), var(--cell));
    background: var(--surface);
    border: 2px solid var(--rule);
    border-radius: 4px;
    overflow: hidden;
    transition: box-shadow 0.3s;
}

.board--solved {
    box-shadow: 0 0 0 3px color-mix(in srgb, var(--success) 55%, transparent);
}

.cell {
    width: var(--cell);
    height: var(--cell);
    border: 0;
    border-right: 1px solid var(--line);
    border-bottom: 1px solid var(--line);
    background: transparent;
    color: var(--entry);
    font: inherit;
    font-size: 1.15rem;
    text-align: center;
    caret-color: transparent;
    transition: background 0.15s, color 0.15s;
}

.cell--box-right {
    border-right: 2px solid var(--rule);
}

.cell--box-bottom {
    border-bottom: 2px solid var(--rule);
}

.cell--given {
    color: var(--given);
    font-weight: 650;
    cursor: default;
}

.cell:not(.cell--given):hover {
    background: color-mix(in srgb, var(--accent) 8%, transparent);
}

.cell:focus {
    outline: none;
    background: color-mix(in srgb, var(--accent) 16%, transparent);
}

.cell--conflict {
    background: var(--conflict-bg);
    color: var(--conflict-fg);
}

.cell--wrong {
    background: var(--wrong-bg);
    color: var(--wrong-fg);
}

.status {
    margin: 0;
    color: var(--muted);
    font-size: 0.9rem;
    font-variant-numeric: tabular-nums;
}

.hint {
    margin: 0;
    color: var(--muted);
    font-size: 0.8rem;
    opacity: 0.75;
}

main {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 0.85rem;
}

.toasts {
    position: fixed;
    right: 1rem;
    bottom: 1rem;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
    z-index: 10;
}

.toast {
    padding: 0.7rem 1rem;
    border-radius: var(--radius);
    border-left: 3px solid var(--accent);
    background: var(--surface);
    color: var(--text);
    font-size: 0.9rem;
    box-shadow: 0 6px 20px rgb(0 0 0 / 0.14);
    cursor: pointer;
    opacity: 1;
    transition: opacity 0.25s, transform 0.25s;
}

.toast--leaving {
    opacity: 0;
    transform: translateX(0.75rem);
}

.toast--success {
    border-left-color: var(--success);
}

.toast--error {
    border-left-color: var(--conflict-fg);
}

@media (max-width: 480px) {
    :root {
        --cell: min(38px, 10vw);
    }

    body {
        padding-top: 1.25rem;
    }
}

@media (prefers-reduced-motion: reduce) {
    * {
        transition: none !important;
    }
}