* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: Arial, sans-serif;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #FFD700;
    transition: background-color 0.5s;
}

.container {
    width: 90%;
    max-width: 600px;
    text-align: center;
    padding: 20px;
    background: rgba(255, 255, 255, 0.9);
    border-radius: 20px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
}

h1 {
    color: #1a2a6c;
    margin-bottom: 30px;
    font-size: 2.5em;
    text-shadow: 2px 2px 4px rgba(0,0,0,0.1);
}

.game-section {
    background: white;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}

.hidden {
    display: none;
}

button {
    font-size: 1.5em;
    padding: 15px 40px;
    border: none;
    border-radius: 5px;
    background-color: #4CAF50;
    color: white;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
    box-shadow: 0 4px 15px rgba(0,0,0,0.2);
    transform: translateY(0);
}

button:hover {
    background-color: #45a049;
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0,0,0,0.25);
}

#problem {
    font-size: 2em;
    margin: 20px 0;
}

#choices {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 10px;
    margin-top: 20px;
}

.choice {
    font-size: 1.5em;
    padding: 15px;
    border: 2px solid #ddd;
    border-radius: 5px;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
    background-color: white;
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
    transform: translateY(0);
}

.choice:hover {
    transform: translateY(-2px);
    box-shadow: 0 4px 12px rgba(0,0,0,0.2);
}

#progress {
    font-size: 1.2em;
    margin-bottom: 20px;
}

#timer {
    font-size: 1.5em;
    margin-top: 20px;
    color: #ff6b6b;
    font-weight: bold;
}

@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.05); }
    100% { transform: scale(1); }
}

.correct {
    background-color: #4CAF50 !important;
    color: white;
    animation: pulse 0.5s;
}

.incorrect {
    background-color: #f44336 !important;
    color: white;
    animation: shake 0.5s;
}

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    25% { transform: translateX(-5px); }
    75% { transform: translateX(5px); }
}

.time-warning {
    color: #f44336;
    animation: pulse 1s infinite;
}