* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}
body {
    font-family: 'Nunito', sans-serif;
    background-color: #e0f7fa; 
    color: #333;
    display: flex;
    flex-direction: column; /* Xếp dọc các phần tử */
    justify-content: space-between; /* Đẩy header lên trên, footer xuống dưới */
    align-items: center;
    min-height: 100vh;
    margin: 0;
    padding: 0;
}

.game-container {
    background-color: white;
    max-width: 600px;
    width: 90%;
    padding: 30px;
    border-radius: 20px;
    box-shadow: 0 8px 15px rgba(0,0,0,0.1);
    border: 5px dashed #4dd0e1;
    text-align: center;
    margin: 20px auto;
    flex-grow: 1; /* Căn chỉnh đẩy footer xuống cuối trang */
}

/* --- TRANG TRÍ HEADER & FOOTER --- */
header {
    background-color: #ff6b81;
    color: white;
    width: 100%;
    padding: 15px;
    text-align: center;
    box-shadow: 0 4px 10px rgba(0,0,0,0.1);
    border-bottom: 5px dashed #ff4757;
}

footer {
    background-color: #2d3436;
    color: white;
    width: 100%;
    padding: 15px;
    text-align: center;
    font-weight: bold;
    margin-top: 20px;
}

/* Các đoạn code h1, .score-board, .option-btn... cũ của em giữ nguyên bên dưới nhé! */


h1 {
    color: #00acc1;
    font-size: 2.2rem;
    margin-bottom: 10px;
}

.score-board {
    font-size: 1.2rem;
    color: #e84393;
    font-weight: bold;
    margin-bottom: 20px;
    background-color: #ffebf0;
    display: inline-block;
    padding: 5px 15px;
    border-radius: 15px;
}

#question-text {
    font-size: 1.4rem;
    color: #2d3436;
    margin-bottom: 20px;
    line-height: 1.5;
}

#options-container {
    display: flex;
    flex-direction: column;
    gap: 10px;
    margin-bottom: 20px;
}

.option-btn {
    background-color: #fff;
    color: #00838f;
    border: 3px solid #00acc1;
    padding: 12px;
    font-size: 1.2rem;
    font-weight: bold;
    border-radius: 15px;
    cursor: pointer;
    transition: all 0.2s;
}

.option-btn:hover {
    background-color: #e0f7fa;
    transform: translateX(5px);
}

.option-btn.correct {
    background-color: #81c784;
    border-color: #388e3c;
    color: white;
}

.option-btn.wrong {
    background-color: #ff6b81;
    border-color: #d63031;
    color: white;
}

#feedback {
    font-size: 1.1rem;
    font-weight: bold;
    min-height: 25px;
    margin-bottom: 15px;
}

button {
    background-color: #ffb74d;
    color: white;
    border: none;
    padding: 10px 25px;
    font-size: 1.2rem;
    font-weight: bold;
    border-radius: 20px;
    cursor: pointer;
    box-shadow: 0 4px 0px #f57c00;
}

button:hover {
    transform: translateY(2px);
    box-shadow: 0 2px 0px #f57c00;
}

.back-link {
    display: inline-block;
    margin-top: 15px;
    color: #00acc1;
    font-weight: bold;
    text-decoration: none;
}