body {
    font-family: Arial, sans-serif;
    padding: 20px;
}

/* ===== BÀI 1 ===== */
.btn {
    padding: 12px 25px;
    background: #1e90ff;
    color: white;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    transition: background-color .5s ease;
}

.btn:hover {
    background: orange;
}

/* ===== BÀI 2 ===== */
.gallery {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

.img-box {
    overflow: hidden;
}

.img-box img {
    width: 100%;
    transition: transform .4s ease, box-shadow .4s ease;
}

.img-box img:hover {
    transform: scale(1.1);
    box-shadow: 0 8px 20px rgba(0,0,0,.3);
}

/* ===== BÀI 3 ===== */
.menu {
    list-style: none;
    display: flex;
    gap: 25px;
    padding: 0;
}

.menu a {
    position: relative;
    text-decoration: none;
    color: black;
}

.menu a::after {
    content: "";
    position: absolute;
    left: 0;
    bottom: -5px;
    width: 0;
    height: 2px;
    background: orange;
    transition: width .3s ease;
}

.menu a:hover::after {
    width: 100%;
}

/* ===== BÀI 4 ===== */
.cards {
    display: flex;
    gap: 20px;
}

.card {
    width: 300px;
    padding: 15px;
    border-radius: 10px;
    box-shadow: 0 4px 10px rgba(0,0,0,.15);
    transition: transform .3s ease, box-shadow .3s ease;
}

.card img {
    width: 100%;
    border-radius: 8px;
}

.card:hover {
    transform: translateY(-10px);
    box-shadow: 0 15px 30px rgba(0,0,0,.3);
}

/* ===== BÀI 5 ===== */
.banner {
    height: 200px;
    background: linear-gradient(135deg, #1e90ff, orange);
    display: flex;
    justify-content: center;
    align-items: center;
}

.title {
    color: white;
    opacity: 0;
    animation: fadeIn 2s ease forwards;
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}