:root {
    --lime: #CCFF00;
    --purple: #BF00FF;
    --white: #FFFFFF;
    --black: #000000;
    --border: 5px solid #000;
    --shadow: 6px 6px 0px 0px #000;
}

body.light-mode {
    --white: #CCFF00;
    --black: #000;
    --purple: #fff;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Space Grotesk', sans-serif;
}

body {
    background: var(--white);
    color: var(--black);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.game-container {
    background: #fff;
    border: var(--border);
    box-shadow: 12px 12px 0px 0px #000;
    padding: 2rem;
    max-width: 900px;
    width: 100%;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 2rem;
}

h1 {
    font-size: 3rem;
    font-weight: 800;
    background: var(--purple);
    color: #fff;
    display: inline-block;
    padding: 5px 15px;
    border: var(--border);
}

.back-btn {
    display: block;
    margin-top: 10px;
    font-weight: 700;
    color: #000;
    text-decoration: underline;
}

.status-bar {
    display: flex;
    gap: 15px;
    margin-bottom: 1rem;
}

.status-item {
    border: var(--border);
    padding: 8px 15px;
    font-weight: 800;
    background: var(--lime);
}

.main-layout {
    display: flex;
    gap: 2rem;
}

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    width: 500px;
    height: 500px;
    background: #000;
    gap: 2px;
    border: var(--border);
}

.cell {
    background: #fff;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2rem;
    font-weight: 800;
    cursor: pointer;
}

.cell.selected { background: var(--lime); }
.cell.highlighted { background: #eee; }
.cell.given { color: #555; background: #fafafa; }
.cell.wrong { background: #ff4b4b; color: #fff; }
.cell.correct { color: var(--purple); }

/* Subgrid borders */
.cell:nth-child(3n) { border-right: 4px solid #000; }
.cell:nth-child(9n) { border-right: none; }
.sudoku-grid > .cell:nth-child(n+19):nth-child(-n+27),
.sudoku-grid > .cell:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 4px solid #000;
}

.num-pad {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 10px;
}

.num-btn {
    width: 70px;
    height: 70px;
    border: var(--border);
    box-shadow: var(--shadow);
    background: #fff;
    font-size: 1.5rem;
    font-weight: 800;
    cursor: pointer;
}

.num-btn:active { transform: translate(3px, 3px); box-shadow: 2px 2px 0px #000; }
.num-btn:hover { background: var(--lime); }

#reboot-btn {
    width: 100%;
    margin-top: 20px;
    height: 60px;
    background: var(--purple);
    color: #fff;
}

#start-modal {
    position: fixed;
    inset: 0;
    background: var(--lime);
    z-index: 1000;
    display: flex;
    align-items: center;
    justify-content: center;
}

.modal-content {
    background: #fff;
    border: var(--border);
    box-shadow: 15px 15px 0px 0px #000;
    padding: 3rem;
    text-align: center;
}

@media (max-width: 800px) {
    .main-layout { flex-direction: column; align-items: center; }
    .sudoku-grid { width: 90vw; height: 90vw; }
}