:root {
    --primary: #6366f1;
    --primary-light: #818cf8;
    --secondary: #a855f7;
    --bg-dark: #0f172a;
    --card-bg: #1e293b;
    --text-light: #f8fafc;
    --text-muted: #94a3b8;
    --glass: rgba(30, 41, 59, 0.7);
    --glass-border: rgba(255, 255, 255, 0.1);
    --thick-border: 4px solid #475569;
}

body {
    margin: 0;
    padding: 0;
    font-family: 'Outfit', sans-serif;
    color: var(--text-light);
    background-color: var(--bg-dark);
}

.sudoku-game-container {
    max-width: 550px;
    margin: 80px auto 20px auto;
    padding: 24px;
    background: var(--card-bg);
    border-radius: 24px;
    box-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    border: 1px solid var(--glass-border);
    position: relative;
    min-width: 320px;
}

.sudoku-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 24px;
}

.sudoku-header h1 {
    margin: 0;
    font-size: 1.8rem;
    display: flex;
    align-items: center;
    gap: 12px;
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.sudoku-game-icon-small {
    width: 32px;
    height: 32px;
}

.sudoku-back-btn {
    padding: 10px 20px;
    background: rgba(51, 65, 85, 0.5);
    border: 1px solid var(--glass-border);
    border-radius: 14px;
    color: var(--text-light);
    cursor: pointer;
    font-weight: 500;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.sudoku-back-btn:hover {
    background: rgba(51, 65, 85, 0.8);
    transform: translateX(-5px);
}

.sudoku-game-info {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: rgba(15, 23, 42, 0.6);
    padding: 15px 25px;
    border-radius: 18px;
    margin-bottom: 24px;
    border: 1px solid var(--glass-border);
}

.sudoku-stats {
    display: flex;
    gap: 30px;
    font-weight: 700;
    font-size: 1.1rem;
}

.sudoku-diff-badge {
    padding: 6px 14px;
    border-radius: 20px;
    font-size: 0.8rem;
    font-weight: 800;
    text-transform: uppercase;
    letter-spacing: 0.5px;
    background: var(--primary);
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.2);
}

.sudoku-diff-badge.easy {
    background: #22c55e;
}

.sudoku-diff-badge.medium {
    background: #eab308;
}

.sudoku-diff-badge.hard {
    background: #ef4444;
}

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    border: var(--thick-border);
    background: #334155;
    gap: 1.5px;
    margin-bottom: 24px;
    aspect-ratio: 1/1;
    width: 100%;
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 15px 35px rgba(0, 0, 0, 0.3);
}

.sudoku-cell {
    background: var(--card-bg);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.6rem;
    font-weight: 700;
    cursor: pointer;
    position: relative;
    transition: all 0.15s cubic-bezier(0.4, 0, 0.2, 1);
    user-select: none;
}

.sudoku-cell:hover {
    background: #2d3748;
    z-index: 2;
}

.sudoku-cell.selected {
    background: rgba(99, 102, 241, 0.35) !important;
    box-shadow: inset 0 0 0 2px var(--primary);
}

.sudoku-cell.highlighted {
    background: rgba(99, 102, 241, 0.12);
}

.sudoku-cell.same-number {
    background: rgba(168, 85, 247, 0.3);
    color: var(--secondary);
}

.sudoku-cell.fixed {
    color: #94a3b8;
    background: rgba(15, 23, 42, 0.2);
}

.sudoku-cell.wrong {
    color: #ef4444;
    background: rgba(239, 68, 68, 0.1);
    animation: shake 0.4s ease-in-out;
}

@keyframes shake {

    0%,
    100% {
        transform: translateX(0);
    }

    25% {
        transform: translateX(-4px);
    }

    75% {
        transform: translateX(4px);
    }
}

/* Sub-grid borders */
.sudoku-cell:nth-child(3n) {
    border-right: 2px solid #475569;
}

.sudoku-cell:nth-child(9n) {
    border-right: none;
}

.sudoku-grid>div:nth-child(n+19):nth-child(-n+27),
.sudoku-grid>div:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 2px solid #475569;
}

.notes-container {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    width: 100%;
    height: 100%;
    font-size: 0.65rem;
    padding: 3px;
    pointer-events: none;
    opacity: 0.8;
}

.note {
    display: flex;
    justify-content: center;
    align-items: center;
    color: var(--text-muted);
}

.sudoku-number-buttons {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    gap: 12px;
    margin-top: 24px;
}

.sudoku-num-btn {
    padding: 14px;
    background: #334155;
    border: 1px solid var(--glass-border);
    border-radius: 14px;
    color: white;
    font-size: 1.3rem;
    font-weight: 800;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    justify-content: center;
    align-items: center;
}

.sudoku-num-btn:hover {
    background: #475569;
    transform: translateY(-3px);
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
}

.sudoku-num-btn.active-note {
    background: var(--primary);
    box-shadow: 0 10px 20px -5px rgba(99, 102, 241, 0.4);
    border-color: var(--primary-light);
}

.sudoku-action-btn {
    background: #1e293b;
    font-size: 1.1rem;
}

/* Modal and Message */
.sudoku-modal,
.sudoku-message {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(15, 23, 42, 0.96);
    backdrop-filter: blur(10px);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 100;
    border-radius: 24px;
    animation: fadeIn 0.3s ease-out;
}

.sudoku-modal-content {
    background: var(--card-bg);
    padding: 40px;
    border-radius: 32px;
    width: 90%;
    max-width: 440px;
    text-align: center;
    border: 1px solid var(--glass-border);
    box-shadow: 0 30px 60px -12px rgba(0, 0, 0, 0.6);
}

.sudoku-input-group {
    margin-bottom: 24px;
    text-align: left;
}

.sudoku-input-group label {
    display: block;
    margin-bottom: 10px;
    color: var(--text-muted);
    font-size: 0.9rem;
    font-weight: 500;
}

.sudoku-input-group input,
.sudoku-input-group select {
    width: 100%;
    padding: 14px 18px;
    background: var(--bg-dark);
    border: 1px solid var(--glass-border);
    border-radius: 14px;
    color: white;
    font-family: inherit;
    font-size: 1rem;
    outline: none;
    transition: all 0.3s;
}

.sudoku-input-group input:focus,
.sudoku-input-group select:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 4px rgba(99, 102, 241, 0.1);
}

.sudoku-btn-start {
    width: 100%;
    padding: 18px;
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
    color: white;
    border: none;
    border-radius: 18px;
    font-weight: 800;
    font-size: 1.1rem;
    cursor: pointer;
    box-shadow: 0 10px 25px -5px rgba(99, 102, 241, 0.4);
    transition: all 0.3s ease;
}

.sudoku-btn-start:hover {
    transform: translateY(-2px);
    box-shadow: 0 15px 30px -5px rgba(99, 102, 241, 0.5);
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: scale(0.95);
    }

    to {
        opacity: 1;
        transform: scale(1);
    }
}

.hidden {
    display: none !important;
}

@media (max-width: 600px) {
    :root {
        --cell-size: 35px;
    }

    .sudoku-game-container {
        padding: 16px;
        margin: 80px 10px;
    }

    .sudoku-stats {
        gap: 15px;
        font-size: 1rem;
    }

    .sudoku-cell {
        font-size: 1.25rem;
    }

    .sudoku-num-btn {
        padding: 10px;
        font-size: 1.1rem;
    }
}
/* Efecto de error - Vibración y color rojo */
@keyframes shake {
    0%, 100% { transform: translateX(0); }
    10%, 30%, 50%, 70%, 90% { transform: translateX(-5px); }
    20%, 40%, 60%, 80% { transform: translateX(5px); }
}

.error-shake {
    animation: shake 0.5s ease-in-out;
}

.error-flash {
    background-color: rgba(239, 68, 68, 0.3) !important;
    transition: background-color 0.5s ease-out;
}