:root {
    --border-color: #333;
    --accent-color: #FF4136;
    --error-color: #FF4136;
    --correct-color: #00FFFF;
    --prefilled-text: #E0E0E0;
    --user-text: #FFFFFF;
    --selected-bg: #4a2a2a;
    --highlight-bg: #3a2a2a;
}
body {
    background-color: #000000;
    color: var(--prefilled-text);
    font-family: Arial, Helvetica, sans-serif;
    margin: 0;
    overflow: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    -webkit-tap-highlight-color: transparent;
}
.hidden {
    display: none !important;
}
a.website-link-icon {
    position: fixed;
    top: 33px;
    right: 40px;
    width: 32px;
    height: 32px;
    z-index: 101;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='24' height='24' viewBox='0 0 24 24' fill='none' stroke='%23a0a0a0' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='M18 13v6a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2V8a2 2 0 0 1 2-2h6'%3E%3C/path%3E%3Cpolyline points='15 3 21 3 21 9'%3E%3C/polyline%3E%3Cline x1='10' y1='14' x2='21' y2='3'%3E%3C/line%3E%3C/svg%3E");
    background-size: contain;
    transition: transform 0.2s;
}
a.website-link-icon:hover {
    transform: scale(1.1);
}
#difficultyOverlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.9);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 100;
}
.modal {
    background-color: #1a1a1a;
    padding: 50px 80px;
    border-radius: 15px;
    text-align: center;
}
.modal h1 {
    font-size: 64px;
    color: var(--accent-color);
    margin: 0 0 10px 0;
    font-weight: bold;
}
.modal h2 {
    font-size: 32px;
    margin: 0 0 40px 0;
    font-weight: normal;
    color: #c0c0c0;
}
.modal-buttons {
    display: flex;
    gap: 25px;
}
#gameContainer {
    display: flex;
    flex-direction: column;
    width: 100%;
    height: 100%;
}
#topBar {
    display: grid;
    grid-template-columns: auto 1fr auto;
    align-items: center;
    padding: 0 40px;
    height: 100px;
    box-sizing: border-box;
    width: 100%;
}
#backButton {
    justify-self: start;
}
.title-container {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 15px;
}
h3 {
    font-size: 38px;
    margin: 0;
    font-weight: normal;
    text-align: center;
}
#pauseMessage {
    color: var(--error-color);
    font-size: 24px;
    font-weight: bold;
    margin-left: 30px;
}
#controls {
    display: flex;
    align-items: center;
    gap: 20px;
    font-size: 20px;
    justify-self: end;
    margin-right: 50px;
}
#winMessage {
    font-size: 20px;
    font-weight: bold;
}
#sudoku-board {
    display: grid;
    grid-template-columns: repeat(9, minmax(0, 1fr));
    grid-template-rows: repeat(9, minmax(0, 1fr));
    width: 90vmin;
    max-width: 540px;
    height: 90vmin;
    max-height: 540px;
    margin: 20px auto;
    border: 3px solid var(--accent-color);
    box-sizing: border-box;
}
.cell {
    border: 1px solid var(--border-color);
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 2.5rem;
    font-weight: bold;
    cursor: pointer;
    user-select: none;
    transition: background-color 0.2s;
}
.cell.prefilled {
    color: var(--prefilled-text);
    cursor: default;
}
.cell.user-input { color: var(--user-text); }
.cell.selected { background-color: var(--selected-bg); }
.cell.correct { color: var(--correct-color); }
.cell.incorrect { color: var(--error-color) !important; }
.cell.highlighted { background-color: var(--highlight-bg); }
.cell:nth-child(3n) { border-right: 2px solid var(--accent-color); }
.cell:nth-child(9n) { border-right: none; }
.row-boundary { border-top: 2px solid var(--accent-color); }
#number-pad {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin: 0 auto 20px auto;
}
.num-btn {
    width: 50px;
    height: 50px;
    font-size: 24px;
}
.num-btn.disabled {
    background-color: #555;
    color: #888;
    cursor: not-allowed;
}
button {
    color: #E0E0E0;
    background-color: #303030;
    border: none;
    font-size: 20px;
    padding: 10px 20px;
    border-radius: 10px;
    cursor: pointer;
    transition: background-color 0.2s;
}
button:hover:not(:disabled) { background-color: #454545; }
button:disabled {
    background-color: #202020;
    color: #777;
    cursor: not-allowed;
}
@media (max-width: 768px) {
    body {
        display: block;
    }
    h3 {
        font-size: 28px;
    }
    #controls {
        font-size: 14px;
        gap: 8px;
        margin-right: 25px;
    }
    button {
        font-size: 16px;
        padding: 8px 12px;
    }
    #backButton {
        font-size: 14px;
    }
    .website-link-icon {
        right: 15px;
        top: 35px;
    }
    #topBar {
        padding: 0 15px;
        height: 80px;
    }
    .modal {
        padding: 30px 40px;
    }
    #sudoku-board {
        width: 95vmin;
        height: 95vmin;
        margin-top: 5px;
    }
    .cell {
        font-size: 1.8rem;
    }
    #number-pad {
        gap: 5px;
    }
    .num-btn {
        width: 38px;
        height: 38px;
        font-size: 20px;
    }
}