body {
    margin: 0;
    overflow: hidden;
    background-color: #1a1a1a;
    /* Dark background */
    color: white;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

#canvas-container {
    width: 100vw;
    height: 100vh;
    display: block;
}

.home-link {
    position: absolute;
    top: 20px;
    left: 20px;
    color: #fff;
    text-decoration: none;
    background: rgba(0, 0, 0, 0.5);
    padding: 8px 12px;
    border-radius: 4px;
    z-index: 1000;
    font-weight: bold;
    transition: background 0.2s;
}

.home-link:hover {
    background: rgba(0, 0, 0, 0.8);
}

#ui-container {
    position: absolute;
    top: 20px;
    right: 20px;
    width: 320px;
    background: rgba(0, 0, 0, 0.7);
    padding: 20px;
    border-radius: 8px;
    backdrop-filter: blur(5px);
    z-index: 100;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
}

.problem-box h2 {
    margin-top: 0;
    font-size: 1.2em;
    border-bottom: 1px solid #444;
    padding-bottom: 10px;
}

.options {
    display: flex;
    flex-direction: column;
    gap: 8px;
    margin: 15px 0;
}

.option-btn {
    background: #333;
    border: 1px solid #555;
    color: white;
    padding: 8px;
    border-radius: 4px;
    cursor: pointer;
    text-align: left;
    transition: all 0.2s;
}

.option-btn:hover {
    background: #444;
    border-color: #666;
}

.option-btn.correct {
    background: #28a745;
    border-color: #28a745;
}

.option-btn.incorrect {
    background: #dc3545;
    border-color: #dc3545;
}

.controls {
    margin-top: 20px;
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.controls button {
    background: #007bff;
    border: none;
    color: white;
    padding: 8px 12px;
    border-radius: 4px;
    cursor: pointer;
    font-weight: 500;
}

.controls button:hover {
    background: #0069d9;
}

#feedback {
    margin-top: 10px;
    padding: 10px;
    background: rgba(255, 255, 255, 0.1);
    border-radius: 4px;
    font-size: 0.9em;
    line-height: 1.4;
}

.hidden {
    display: none;
}

.instruction {
    margin-top: 15px;
    font-size: 0.8em;
    color: #aaa;
    text-align: center;
}