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

body {
    font-family: 'Segoe UI', Tahoma, Arial, sans-serif;
    background: #f4f6f8;
    color: #222;
}

/* ===== HEADER ===== */
.header {
    background: linear-gradient(135deg, #ff7a00, #ff9a3c);
    color: #fff;
    padding: 25px 40px;
}

.header h1 {
    font-size: 28px;
    margin-bottom: 6px;
}

.header p {
    opacity: 0.9;
}

/* ===== CONTAINER ===== */
.container {
    max-width: 1100px;
    margin: 30px auto;
    padding: 0 20px;
}

/* ===== CARD ===== */
.card {
    background: #fff;
    border-radius: 10px;
    padding: 25px;
    box-shadow: 0 10px 30px rgba(0,0,0,.08);
    margin-bottom: 30px;
}

.card h2 {
    margin-bottom: 15px;
    font-size: 22px;
}

/* ===== GRADE GRID ===== */
.grade-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 15px;
    margin-top: 15px;
}

.grade-grid a {
    display: block;
    background: #fff;
    border: 2px solid #ff7a00;
    color: #ff7a00;
    text-align: center;
    padding: 14px;
    border-radius: 8px;
    font-weight: 600;
    text-decoration: none;
    transition: .25s;
}

.grade-grid a:hover {
    background: #ff7a00;
    color: #fff;
    transform: translateY(-3px);
}

/* ===== LOGIN BUTTON ===== */
.login-box {
    text-align: center;
    margin-top: 20px;
}

.login-box a {
    display: inline-block;
    background: #111;
    color: #fff;
    padding: 12px 25px;
    border-radius: 25px;
    text-decoration: none;
    font-weight: 600;
    transition: .25s;
}

.login-box a:hover {
    background: #ff7a00;
}

/* ===== FOOTER ===== */
.footer {
    text-align: center;
    padding: 20px;
    font-size: 14px;
    color: #777;
}
/* ===== INDEX HERO ===== */
.hero {
    background: linear-gradient(135deg, #ff7a00, #ff9a3c);
    color: #fff;
    padding: 70px 20px;
    text-align: center;
}

.hero h1 {
    font-size: 42px;
    margin-bottom: 15px;
}

.hero p {
    font-size: 18px;
    opacity: 0.95;
    max-width: 800px;
    margin: auto;
}

/* ===== SECTION ===== */
.section {
    max-width: 1200px;
    margin: 50px auto;
    padding: 0 20px;
}

.section-title {
    text-align: center;
    font-size: 28px;
    margin-bottom: 30px;
}

/* ===== FEATURES ===== */
.features {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
    gap: 25px;
}

.feature {
    background: #fff;
    border-radius: 12px;
    padding: 25px;
    box-shadow: 0 8px 25px rgba(0,0,0,.08);
    text-align: center;
}

.feature span {
    font-size: 36px;
}

.feature h3 {
    margin: 15px 0 10px;
}

/* ===== GRADE CARD ===== */
.grade-cards {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: 20px;
}

.grade-card {
    background: #fff;
    border-radius: 14px;
    padding: 25px 10px;
    text-align: center;
    text-decoration: none;
    color: #222;
    box-shadow: 0 6px 18px rgba(0,0,0,.08);
    transition: .25s;
}

.grade-card:hover {
    transform: translateY(-6px);
    box-shadow: 0 12px 30px rgba(0,0,0,.15);
}

.grade-card strong {
    font-size: 26px;
    color: #ff7a00;
}

/* ===== CTA ===== */
.cta {
    background: #111;
    color: #fff;
    padding: 50px 20px;
    text-align: center;
}

.cta a {
    display: inline-block;
    margin: 10px;
    padding: 14px 30px;
    background: #ff7a00;
    color: #fff;
    border-radius: 30px;
    text-decoration: none;
    font-weight: 600;
    transition: .25s;
}

.cta a.secondary {
    background: #fff;
    color: #111;
}

.cta a:hover {
    opacity: 0.9;
}

/* ===== FOOTER ===== */
.footer {
    background: #f1f1f1;
    text-align: center;
    padding: 20px;
    color: #666;
}
body {
    font-family: 'Segoe UI', sans-serif;
    background: linear-gradient(135deg, #667eea, #764ba2);
    margin: 0;
    padding: 0;
}

.student-container {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    color: #333;
}

.student-container h1 {
    color: #fff;
    margin-bottom: 5px;
}

.subtitle {
    color: #e0e0e0;
    margin-bottom: 25px;
}

.exam-card {
    background: #fff;
    padding: 30px 35px;
    width: 100%;
    max-width: 420px;
    border-radius: 14px;
    box-shadow: 0 15px 40px rgba(0,0,0,0.25);
}

.form-group {
    margin-bottom: 18px;
}

.form-group label {
    display: block;
    font-weight: 600;
    margin-bottom: 6px;
}

.form-group select {
    width: 100%;
    padding: 10px;
    border-radius: 8px;
    border: 1px solid #ccc;
    font-size: 15px;
}

.btn-start {
    width: 100%;
    padding: 12px;
    background: #667eea;
    color: #fff;
    border: none;
    border-radius: 10px;
    font-size: 16px;
    font-weight: bold;
    cursor: pointer;
    transition: 0.3s;
}

.btn-start:hover {
    background: #5a67d8;
}

.student-footer {
    margin-top: 20px;
}

.student-footer a {
    color: #fff;
    text-decoration: none;
    opacity: 0.9;
}

.student-footer a:hover {
    text-decoration: underline;
}
.exam-container {
    max-width: 900px;
    margin: 40px auto;
    background: #fff;
    padding: 30px;
    border-radius: 14px;
    box-shadow: 0 15px 40px rgba(0,0,0,0.2);
}

.timer {
    font-size: 18px;
    color: #e53e3e;
    font-weight: bold;
    margin-bottom: 20px;
}

.question-box {
    margin-bottom: 25px;
    padding-bottom: 15px;
    border-bottom: 1px solid #eee;
}
.exam-nav {
    margin-top: 20px;
    text-align: center;
}

.exam-nav button {
    padding: 10px 20px;
    margin: 5px;
    border: none;
    background: #ff7a00;
    color: white;
    border-radius: 6px;
    cursor: pointer;
}

.exam-nav button:hover {
    opacity: 0.9;
}
.page-info {
    font-weight: bold;
    margin: 0 15px;
    display: inline-block;
}
/* ===== MENU NGANG ===== */
.top-menu {
    position: sticky;
    top: 0;
    background: linear-gradient(90deg, #1e3c72, #2a5298);
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 12px 30px;
    z-index: 999;
    box-shadow: 0 2px 8px rgba(0,0,0,0.2);
}

.menu-logo {
    font-size: 20px;
    font-weight: bold;
    color: #fff;
}

.menu-nav a {
    color: #fff;
    margin-left: 25px;
    text-decoration: none;
    font-size: 16px;
    position: relative;
    padding-bottom: 5px;
    transition: 0.3s;
}

.menu-nav a:hover {
    opacity: 0.85;
}

/* gạch chân khi hover */
.menu-nav a::after {
    content: '';
    position: absolute;
    left: 0;
    bottom: 0;
    width: 0;
    height: 2px;
    background: #ffdd57;
    transition: width 0.3s;
}

.menu-nav a:hover::after,
.menu-nav a.active::after {
    width: 100%;
}

/* ===== RESPONSIVE ===== */
@media (max-width: 768px) {
    .top-menu {
        flex-direction: column;
        align-items: flex-start;
    }

    .menu-nav {
        margin-top: 10px;
    }

    .menu-nav a {
        margin: 0 15px 0 0;
    }
}