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

body {
    font-family: system-ui, sans-serif;
    background: #f0f2f5;
    color: #1a1a2e;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 2rem 1rem;
    gap: 1.5rem;
}

h1 {
    font-size: 1.6rem;
    font-weight: 700;
    letter-spacing: -0.5px;
}

h1 span {
    color: #4361ee;
}

/* ── Controls ── */
.controls {
    display: flex;
    flex-wrap: wrap;
    gap: .75rem;
    align-items: center;
    justify-content: center;
}

select, button, input[type="text"] {
    font-size: .9rem;
    padding: .45rem .85rem;
    border-radius: 8px;
    border: 1.5px solid #cdd;
    background: #fff;
    cursor: pointer;
    transition: border-color .15s, background .15s;
}

select:focus, input[type="text"]:focus { outline: none; border-color: #4361ee; }

button {
    background: #4361ee;
    color: #fff;
    border-color: #4361ee;
    font-weight: 600;
}
button:hover  { background: #3451d1; }
button:active { background: #2a40b8; }
button:disabled { background: #a0aec0; border-color: #a0aec0; cursor: not-allowed; }

button.secondary {
    background: #fff;
    color: #4361ee;
    border-color: #4361ee;
}
button.secondary:hover { background: #eef0fd; }

input[type="text"] {
    width: 26ch;
    font-family: monospace;
    letter-spacing: 1px;
}

/* ── Speed slider ── */
.speed-wrap {
    display: flex;
    align-items: center;
    gap: .5rem;
    font-size: .85rem;
    color: #555;
}
input[type="range"] { width: 90px; accent-color: #4361ee; }

/* ── Main layout ── */
.main {
    display: flex;
    flex-wrap: wrap;
    gap: 2rem;
    justify-content: center;
    align-items: flex-start;
}

/* ── Sudoku grid ── */
.board-wrap { display: flex; flex-direction: column; align-items: center; gap: .5rem; }
.board-label { font-size: .8rem; color: #888; text-transform: uppercase; letter-spacing: 1px; }

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    border: 3px solid #1a1a2e;
    border-radius: 4px;
    overflow: hidden;
    width: min(90vw, 400px);
    aspect-ratio: 1;
}

.cell {
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: clamp(.9rem, 2.5vw, 1.3rem);
    font-weight: 500;
    border: 1px solid #ccc;
    background: #fff;
    transition: background .12s, color .12s;
    cursor: default;
    user-select: none;
    aspect-ratio: 1;
    min-height: 0;
    min-width: 0;
}

/* Box borders */
.cell[data-col="2"], .cell[data-col="5"] { border-right: 2.5px solid #1a1a2e; }
.cell[data-row="2"], .cell[data-row="5"] { border-bottom: 2.5px solid #1a1a2e; }

/* Cell states */
.cell.given    { color: #1a1a2e; font-weight: 700; background: #f7f7f7; }
.cell.solved   { color: #4361ee; }
.cell.active   { background: #dce3ff; color: #2a40b8; }
.cell.conflict { background: #ffe0e0; color: #c0392b; }
.cell.flash    { animation: flash .3s ease; }

@keyframes flash {
    0%   { background: #b8f0c8; }
    100% { background: #fff; }
}

/* ── Info panel ── */
.info-panel {
    display: flex;
    flex-direction: column;
    gap: 1rem;
    min-width: 200px;
    max-width: 260px;
}

.stat-box {
    background: #fff;
    border-radius: 12px;
    padding: 1rem 1.2rem;
    box-shadow: 0 1px 4px rgba(0,0,0,.08);
}

.stat-box h3 { font-size: .75rem; text-transform: uppercase; letter-spacing: 1px; color: #888; margin-bottom: .6rem; }

.stat-row {
    display: flex;
    justify-content: space-between;
    font-size: .9rem;
    padding: .2rem 0;
    border-bottom: 1px solid #f0f0f0;
}
.stat-row:last-child { border-bottom: none; }
.stat-row .val { font-weight: 600; color: #4361ee; }

/* ── Status bar ── */
.status {
    font-size: .9rem;
    padding: .4rem 1rem;
    border-radius: 8px;
    background: #fff;
    box-shadow: 0 1px 4px rgba(0,0,0,.08);
    min-width: 200px;
    text-align: center;
}
.status.ok      { color: #27ae60; font-weight: 600; }
.status.error   { color: #c0392b; font-weight: 600; }
.status.running { color: #4361ee; }

/* ── Footer ── */
footer {
    font-size: .82rem;
    color: #888;
    padding: .5rem 0 1rem;
}
footer a { color: #4361ee; text-decoration: none; }
footer a:hover { text-decoration: underline; }

/* ── Preset list ── */
.presets { display: flex; flex-wrap: wrap; gap: .4rem; justify-content: center; }
.presets button {
    font-size: .78rem;
    padding: .3rem .65rem;
    background: #fff;
    color: #333;
    border-color: #cdd;
    font-weight: 500;
}
.presets button:hover { border-color: #4361ee; color: #4361ee; background: #eef0fd; }