/* Cấu hình chung */
body {
    font-family: Arial, sans-serif;
    transition: background 0.3s, color 0.3s;
    margin: 0;
    padding: 0;
}

section {
    min-height: 100vh;
    padding: 100px 50px;
    border-bottom: 1px dashed #ccc;
}

/* Bài 1: Dark mode */
body.dark {
    background: #222;
    color: #fff;
}

/* Bài 2: Menu Fixed & Active */
#navbar {
    position: fixed;
    top: 0; width: 100%;
    background: #333;
    padding: 10px 0;
    z-index: 1000;
}
#navbar ul {
    display: flex;
    justify-content: center;
    list-style: none;
    margin: 0;
}
#navbar a {
    color: white;
    text-decoration: none;
    padding: 10px 20px;
}
#navbar a.active {
    background: orange;
    border-radius: 5px;
}

/* Bài 3: Scroll Reveal */
.box {
    width: 200px;
    height: 150px;
    background: skyblue;
    margin: 20px 0;
    display: flex;
    align-items: center;
    justify-content: center;
    /* Trạng thái ẩn */
    opacity: 0;
    transform: translateY(30px);
    transition: all 0.6s ease-out;
}
.box.show {
    opacity: 1;
    transform: translateY(0);
}

/* Bài 4: Jump Animation */
.jump {
    padding: 15px 30px;
    font-size: 18px;
    cursor: pointer;
}
.animate {
    animation: jump-effect 0.5s ease;
}
@keyframes jump-effect {
    0% { transform: translateY(0); }
    50% { transform: translateY(-10px); }
    100% { transform: translateY(0); }
}

/* Bài 5: Follow Cursor */
.circle {
    position: fixed;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    background: red;
    pointer-events: none; /* Tránh cản trở việc click các nút bên dưới */
    z-index: 9999;
    top: 0; left: 0;
    transition: transform 0.1s ease-out;
}