:root {
    --primary-color: #3d99f5; /* Blue for buttons */
    --secondary-color: #e0f2fe; /* Light blue for solved cells */
    --background-color: #f9f9f9;
    --text-primary: #1f2937;
    --text-secondary: #6b7280;
    --accent-color: #bfdbfe;
    --solved-color: #d1e7dd; /* Light green for input cells */
}

body {
    font-family: 'Manrope', sans-serif;
    background-color: var(--background-color);
    color: var(--text-primary);
    margin: 0;
    padding: 0;
}

.button_primary {
    background-color: var(--primary-color); /* bg-[var(--primary-color)] */
    color: white; /* text-white */
    border-radius: 0.375rem; /* rounded-md (6px) */
    padding-left: 1rem; /* px-4 */
    padding-right: 1rem; /* px-4 */
    padding-top: 0.5rem; /* py-2 */
    padding-bottom: 0.5rem; /* py-2 */
    transition: background-color 0.2s; /* Smooth hover transition */
}

.button_primary:hover {
    background-color: #2563eb; /* hover:bg-blue-600 */
}

.button_primary:focus {
    outline: none; /* focus:outline-none */
    box-shadow: 0 0 0 2px rgba(59, 130, 246, 0.5); /* focus:ring-2 focus:ring-blue-500 focus:ring-opacity-50 */
}

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    grid-template-rows: repeat(9, 1fr);
    border: 3px solid var(--text-primary);
    aspect-ratio: 1;
    width: 100%;
    max-width: 400px;
    margin: 0 auto;
    border-radius: 8px;
    background-color: white;
}

.sudoku-cell {
    border: 1px solid var(--accent-color);
    display: flex;
    align-items: center;
    justify-content: center;
    min-width: 0;
}

.sudoku-cell input {
    width: 100%;
    height: 100%;
    text-align: center;
    border: none;
    background-color: transparent;
    font-size: 1.25rem;
    color: var(--text-primary);
    padding: 0.25rem;
    box-sizing: border-box;
}

.sudoku-cell input:focus {
    outline: none;
    background-color: var(--solved-color); /* Light green for user input */
}

.sudoku-cell:nth-child(3n):not(:nth-child(9n)) {
    border-right: 2px solid var(--text-primary);
}

.sudoku-grid > div:nth-child(n+28):nth-child(-n+36),
.sudoku-grid > div:nth-child(n+55):nth-child(-n+63) {
    border-top: 2px solid var(--text-primary);
}

.solved {
    background-color: var(--secondary-color) !important; /* Light blue for solved cells */
}

.error {
    background-color: #fee2e2;
}