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

:root {
    --bg-primary: #0f172a;
    --bg-secondary: #1e293b;
    --bg-tertiary: #334155;
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --accent: #06b6d4;
    --accent-hover: #0891b2;
    --accent-light: rgba(6, 182, 212, 0.2);
    --border: #475569;
    --border-thick: #64748b;
    --success: #10b981;
    --warning: #f59e0b;
    --danger: #ef4444;
    --cell-bg: #ffffff;
    --cell-border: #cbd5e1;
    --cell-border-thick: #1e293b;
    --cell-hover: #d5ffe9;
    --cell-valid: #bbf7d0;
    --cell-recent: #bfdbfe;
    --prefilled-badge: #ef4444;

    --player-1: #3584e4;
    --player-2: #813d9c;
    --player-3: #c01c28;
    --player-4: #366100;
}

body {
    font-family:
        -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu,
        Cantarell, sans-serif;
    background: linear-gradient(
        135deg,
        var(--bg-primary) 0%,
        var(--bg-secondary) 100%
    );
    color: var(--text-primary);
    overflow: hidden;
    touch-action: manipulation;
    -webkit-tap-highlight-color: transparent;
    min-height: 100vh;
}

#app {
    width: 100vw;
    height: 100vh;
    display: flex;
    flex-direction: column;
    overflow: hidden;
}

/* Game UI */
#gameUI {
    display: flex;
    flex-direction: column;
    height: 100vh;
    padding: 0.8rem;
    gap: 0.8rem;
}

#header {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

#header h1 {
    font-size: clamp(16px, 4vw, 1.8rem);
    font-weight: 700;
    color: var(--accent);
    text-shadow: 0 2px 4px rgba(0, 0, 0, 0.3);
    margin: 0;
}

#scores {
    display: flex;
    gap: 1rem;
    justify-content: center;
}

.score-item {
    padding: 0.5rem 1rem;
    background: var(--bg-tertiary);
    border-radius: 8px;
    border-left: 4px solid;
    font-weight: 700;
    font-size: 1rem;
    box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
    transition: transform 0.2s;
}

.score-item.player-1 {
    border-color: var(--player-1);
}

.score-item.player-2 {
    border-color: var(--player-2);
}

.score-item.player-3 {
    border-color: var(--player-3);
}

.score-item.player-4 {
    border-color: var(--player-4);
}

.score-item.active {
    transform: scale(1.05);
    box-shadow: 0 0 0 3px var(--accent-light);
}

#actions {
    display: flex;
    gap: 0.6rem;
}

.icon-button {
    width: 44px;
    height: 44px;
    background: var(--bg-tertiary);
    border: 2px solid var(--border);
    border-radius: 8px;
    color: var(--text-primary);
    font-size: 1.3rem;
    font-weight: 700;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.2s;
    box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
}

.icon-button:hover {
    background: var(--accent);
    border-color: var(--accent);
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(6, 182, 212, 0.4);
}

/* Board */
#boardContainer {
    flex: 1;
    display: flex;
    align-items: center;
    justify-content: center;
    overflow: auto;
    min-height: 0;
}

#board {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 0;
    background: var(--cell-bg);
    border: 3px solid var(--cell-border-thick);
    border-radius: 16px;
    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
    aspect-ratio: 1;
    width: 100%;
    max-width: min(90vmin, 650px);
    max-height: min(90vmin, 650px);
    overflow: hidden;
}

.cell {
    aspect-ratio: 1;
    border: 2px solid var(--cell-border);
    border-top: 0;
    border-left: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    font-weight: 700;
    font-size: 4vw;
    background: var(--cell-bg);
    transition: background 0.15s;
    position: relative;
    color: #1e293b;
}

/* Thicker borders for 3x3 zones - right borders */
.cell:nth-child(3n) {
    border-right: 3px solid var(--cell-border-thick);
}

/* Thicker borders for 3x3 zones - bottom borders */
.cell:nth-child(n + 19):nth-child(-n + 27),
.cell:nth-child(n + 46):nth-child(-n + 54) {
    border-bottom: 3px solid var(--cell-border-thick);
}

.cell.prefilled {
    background: linear-gradient(135deg, #ffd93d 0%, #ff9a3d 100%);
    font-weight: 900;
}

.cell.prefilled::after {
    content: "+3";
    position: absolute;
    top: 1px;
    right: 1px;
    font-size: clamp(6px, 2vw, 12px);
    font-weight: 700;
    color: var(--prefilled-badge);
    background: rgba(239, 68, 68, 0.1);
    padding: 1px 3px;
    border-radius: 3px;
    z-index: 1;
}

.cell.recent {
    box-shadow: inset 0 0 0 3px rgba(6, 182, 212, 0.6);
}
.cell.empty.valid-placement {
    background: var(--cell-valid);
}

.cell.empty.valid-placement:hover {
    background: var(--cell-hover);
    cursor: pointer;
}

.cell.selected {
    box-shadow: inset 0 0 0 3px var(--accent);
    background: var(--accent-light);
}

.cell.temporary {
    cursor: pointer;
    font-weight: 700;
}

.cell.error {
    animation: shake 0.3s;
    background: rgba(239, 68, 68, 0.2);
}

.cell.player-1 {
    background-color: var(--player-1);
}

.cell.player-2 {
    background-color: var(--player-2);
}

.cell.player-3 {
    background-color: var(--player-3);
}

.cell.player-4 {
    background-color: var(--player-4);
}

@keyframes shake {
    0%,
    100% {
        transform: translateX(0);
    }
    25% {
        transform: translateX(-4px);
    }
    75% {
        transform: translateX(4px);
    }
}

#currentPlayerInfo {
    text-align: center;
    margin-bottom: 0.8rem;
    font-weight: 700;
    font-size: clamp(12px, 6vw, 32px);
    text-shadow: 0 1px 2px rgba(0, 0, 0, 0.3);
}

#currentPlayerInfo.player-1 {
    color: var(--player-1);
}

#currentPlayerInfo.player-2 {
    color: var(--player-2);
}

#currentPlayerInfo.player-3 {
    color: var(--player-3);
}

#currentPlayerInfo.player-4 {
    color: var(--player-4);
}

#letters {
    display: flex;
    justify-content: center;
    gap: 0.6rem;
    margin-bottom: 1rem;
    flex-wrap: wrap;
}

.letter {
    width: clamp(40px, 11vw, 55px);
    height: clamp(40px, 11vw, 55px);
    background: linear-gradient(
        135deg,
        var(--bg-tertiary) 0%,
        var(--bg-secondary) 100%
    );
    border: 3px solid var(--border);
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 900;
    font-size: clamp(18px, 6vw, 28px);
    cursor: pointer;
    transition: all 0.2s;
    user-select: none;
    box-shadow: 0 3px 8px rgba(0, 0, 0, 0.3);
}

.letter:hover {
    background: linear-gradient(
        135deg,
        var(--accent) 0%,
        var(--accent-hover) 100%
    );
    border-color: var(--accent);
    color: var(--text-primary);
    box-shadow: 0 6px 16px rgba(6, 182, 212, 0.5);
}

.letter.selected {
    background: linear-gradient(
        135deg,
        var(--accent) 0%,
        var(--accent-hover) 100%
    );
    border-color: var(--accent);
    color: var(--text-primary);
    box-shadow: 0 0 0 3px var(--accent-light);
    transform: scale(1.1);
}

.letter.used {
    opacity: 0.4;
    cursor: not-allowed;
}

.letter.used:hover {
    background: linear-gradient(
        135deg,
        var(--bg-tertiary) 0%,
        var(--bg-secondary) 100%
    );
    border-color: var(--border);
    transform: none;
    box-shadow: 0 3px 8px rgba(0, 0, 0, 0.3);
}

#gameActions {
    display: flex;
    justify-content: center;
    gap: 0.8rem;

    .primary-button,
    .secondary-button {
        width: 140px;
    }
}

/* Responsive adjustments */
@media (max-width: 600px) {
    #gameUI {
        padding: 0.5rem;
        gap: 0.5rem;
    }

    .score-item {
        padding: 0.4rem 0.8rem;
        font-size: 0.9rem;
    }

    #availableLetters {
        padding: 0.8rem;
    }

    .icon-button {
        width: 38px;
        height: 38px;
        font-size: 1.1rem;
    }
}

@media (max-height: 650px) {
    #board {
        max-width: min(85vmin, 500px);
        max-height: min(85vmin, 500px);
    }

    .cell {
        font-size: clamp(13px, 3.5vmin, 18px);
    }

    .letter {
        width: 35px;
        height: 35px;
        font-size: 18px;
    }
}

/* Touch improvements */
@media (hover: none) {
    .letter:hover {
        background: linear-gradient(
            135deg,
            var(--bg-tertiary) 0%,
            var(--bg-secondary) 100%
        );
        border-color: var(--border);
        transform: none;
        box-shadow: 0 3px 8px rgba(0, 0, 0, 0.3);
    }

    .letter.used:hover {
        background: linear-gradient(
            135deg,
            var(--bg-tertiary) 0%,
            var(--bg-secondary) 100%
        );
    }

    .icon-button:hover {
        background: var(--bg-tertiary);
        border-color: var(--border);
        transform: none;
        box-shadow: 0 2px 6px rgba(0, 0, 0, 0.2);
    }

    .cell.empty:hover {
        background: var(--cell-bg);
    }

    .cell.empty.valid-placement {
        background: var(--cell-valid);
    }
}

/* Fullscreen */
#app:fullscreen #fullscreenBtn::before {
    content: "⛶";
}