* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', system-ui, sans-serif;
}

body {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    background: #0f172a;
    padding: 2rem;
    color: #e2e8f0;
    position: relative;
    overflow: hidden;
}

.bg-animation {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    z-index: 0;
    overflow: hidden;
}

.bg-gradient {
    position: absolute;
    width: 500px;
    height: 500px;
    border-radius: 50%;
    filter: blur(100px);
    animation: move 15s infinite alternate;
    opacity: 0.5;
}

.gradient-1 {
    background: #3b82f6;
    top: -200px;
    left: -200px;
    animation-delay: -2s;
}

.gradient-2 {
    background: #6366f1;
    bottom: -200px;
    right: -200px;
    animation-delay: -4s;
}

.gradient-3 {
    background: #8b5cf6;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    animation-delay: -6s;
}

@keyframes move {
    0% {
        transform: translate(0, 0) scale(1);
    }

    100% {
        transform: translate(100px, 50px) scale(1.2);
    }
}

.container {
    background: rgba(255, 255, 255, 0.1);
    backdrop-filter: blur(10px);
    border-radius: 1rem;
    border: 1px solid rgba(255, 255, 255, 0.2);
    padding: 2rem;
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.1);
    z-index: 1;
    animation: fadeIn 0.5s ease;
}

@keyframes fadeIn {
    from {
        opacity: 0; transform: translateY(20px);
    }

    to {
        opacity: 1; transform: translateY(0);
    }
}

.header {
    margin-bottom: 2rem;
    text-align: center;
}

h1 {
    color: #f8fafc;
    font-size: 2.5rem;
    margin-bottom: 0.5rem;
    text-shadow: 0 0 10px rgba(59, 130, 246, 0.5);
}

.difficulty {
    margin-bottom: 1rem;
}

.difficulty button {
    padding: 0.5rem 1rem;
    margin: 0 0.25rem;
    border: none;
    border-radius: 0.5rem;
    background: rgba(255, 255, 255, 0.1);
    color: #e2e8f0;
    cursor: pointer;
    transition: all 0.3s;
    backdrop-filter: blur(5px);
}

.difficulty button:hover {
    background: rgba(255, 255, 255, 0.2);
}

.difficulty button.active {
    background: rgba(59, 130, 246, 0.3);
    border: 1px solid rgba(59, 130, 246, 0.5);
}

.controls button {
    padding: 0.5rem 1rem;
    margin: 0 0.25rem;
    border: none;
    border-radius: 0.5rem;
    background: rgba(59, 130, 246, 0.3);
    color: #f8fafc;
    cursor: pointer;
    transition: all 0.3s;
    border: 1px solid rgba(59, 130, 246, 0.5);
}

.controls button:hover {
    background: rgba(59, 130, 246, 0.5);
    transform: translateY(-2px);
}

.grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 1px;
    background: rgba(203, 213, 225, 0.1);
    padding: 1px;
    border-radius: 0.5rem;
    overflow: hidden;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.2);
}

.cell {
    width: 40px;
    height: 40px;
    background: rgba(255, 255, 255, 0.05);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 1.25rem;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s;
    color: #e2e8f0;
}

.cell:hover {
    background: rgba(255, 255, 255, 0.1);
}

.cell.prefilled {
    color: #94a3b8;
    font-weight: 600;
}

.cell.selected {
    background: rgba(59, 130, 246, 0.2);
    border: 1px solid rgba(59, 130, 246, 0.5);
}

.cell.error {
    color: #ef4444;
}

.cell:nth-child(9n+1), .cell:nth-child(9n+2), .cell:nth-child(9n+3) {
    border-right: 2px solid rgba(203, 213, 225, 0.2);
}

.cell:nth-child(n+19):nth-child(-n+27), .cell:nth-child(n+46):nth-child(-n+54) {
    border-bottom: 2px solid rgba(203, 213, 225, 0.2);
}

.status {
    margin-top: 1rem;
    font-size: 1.125rem;
    color: #94a3b8;
    text-align: center;
}

.numpad {
    margin-top: 1rem;
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 0.5rem;
}

.numpad button {
    padding: 0.75rem;
    border: none;
    border-radius: 0.5rem;
    background: rgba(255, 255, 255, 0.1);
    color: #e2e8f0;
    font-size: 1.125rem;
    cursor: pointer;
    transition: all 0.3s;
    backdrop-filter: blur(5px);
}

.numpad button:hover {
    background: rgba(255, 255, 255, 0.2);
    transform: translateY(-2px);
}

@media (max-width: 480px) {
    .cell {
        width: 35px;
        height: 35px;
        font-size: 1rem;
    }

    .container {
        padding: 1rem;
    }
}