body {
    margin: 0;
    font-family: Arial;
    background: #f4f6f9;
}

/* HEADER */
.header {
    background: linear-gradient(45deg, #007bff, #00c6ff);
    color: white;
    text-align: center;
    padding: 25px;
}

/* NAVBAR */
.navbar {
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    background: #333;
}

.navbar a {
    color: white;
    padding: 14px 20px;
    text-decoration: none;
}

.navbar a:hover {
    background: #007bff;
}

/* MAIN */
.main {
    display: flex;
    justify-content: center;
    gap: 20px;
    padding: 20px;
    flex-wrap: wrap;
}

/* SIDEBAR */
.sidebar {
    flex: 1;
    min-width: 250px;
    max-width: 300px;
    background: white;
    padding: 15px;
    border-radius: 10px;
    box-shadow: 0 5px 10px rgba(0,0,0,0.1);
}

/* CONTENT */
.content {
    flex: 3;
    min-width: 300px;
    text-align: center;
}

/* GRID */
.container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 20px;
    margin-top: 30px;
}

.container a {
    display: block;
    padding: 20px;
    background: white;
    border-radius: 12px;
    text-decoration: none;
    color: #007bff;
    font-weight: bold;
    box-shadow: 0 4px 8px rgba(0,0,0,0.1);
    transition: 0.3s;
}

.container a:hover {
    transform: translateY(-5px);
    background: #007bff;
    color: white;
}

/* FOOTER */
.footer {
    margin-top: 40px;
    background: #222;
    color: white;
    text-align: center;
    padding: 20px;
}

/* OVERLAY */
#overlay {
    display: none;
    position: fixed;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    background: rgba(0,0,0,0.5);
    z-index: 999;
}

/* CONTACT FORM */
#contactForm {
    display: none;
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    width: 90%;
    max-width: 400px;
    background: white;
    padding: 20px;
    border-radius: 12px;
    box-shadow: 0 5px 20px rgba(0,0,0,0.3);
    z-index: 1000;
}

.closeBtn {
    float: right;
    cursor: pointer;
    border: none;
    background: red;
    color: white;
    padding: 5px 10px;
}

/* FORM */
input, textarea {
    width: 100%;
    padding: 10px;
    margin: 10px 0;
    border-radius: 5px;
    border: 1px solid #ccc;
    box-sizing: border-box;
}

button {
    padding: 10px;
    background: #007bff;
    color: white;
    border: none;
    border-radius: 5px;
    width: 100%;
}

button:hover {
    background: #0056b3;
}

/* RESPONSIVE */
@media (max-width: 768px) {
    .header h1 {
        font-size: 22px;
    }
}

/* ===== MENU TUẦN 6 ===== */
.menu {
    list-style: none;
    display: flex;
    background: #007bff;
    padding: 0;
}

.menu > li {
    position: relative;
    padding: 15px 20px;
    color: white;
}

/* submenu */
.menu li ul {
    display: none;
    position: absolute;
    top: 100%;
    left: 0;
    background: #007bff;
    list-style: none;
    padding: 0;
    min-width: 150px;
}

.menu li:hover > ul {
    display: block;
}

.menu li ul li {
    padding: 10px;
}

.menu li:hover,
.menu li ul li:hover {
    background: #0056b3;
}

/* nút quay lại */
.back {
    display: inline-block;
    margin-top: 40px;
    padding: 10px 20px;
    background: red;
    color: white;
    text-decoration: none;
    border-radius: 8px;
}

.back:hover {
    background: darkred;
}
/* ===== TUẦN 6 ===== */

.week6 {
    display: grid;
    grid-template-columns: repeat(2, 200px);
    gap: 20px;
    justify-content: center;
    margin-top: 40px;
}

.week6 a {
    display: block;
    padding: 20px;
    background: white;
    color: #007bff;
    text-decoration: none;
    border-radius: 15px;
    text-align: center;
    font-weight: bold;
    box-shadow: 0 5px 10px rgba(0,0,0,0.1);
    transition: 0.3s;
}

.week6 a:hover {
    transform: translateY(-5px);
    background: #007bff;
    color: white;
}