/* Biến CSS */
:root {
    --primary-color: #0A2463;
    --secondary-color: #FFD700;
    --text-color: #333;
    --light-text-color: #f0f0f0;
    --dark-bg: #1a1a1a;
    --light-bg: #ffffff;
}

/* Thiết lập chung */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
}

body {
    font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--light-bg);
}

a {
    text-decoration: none;
    color: var(--primary-color);
}

a:hover {
    color: var(--secondary-color);
}

ul {
    list-style: none;
}

/* Header */
.site-header {
    background-color: var(--primary-color);
    color: var(--light-text-color);
    padding: 1rem 0;
    box-shadow: 0 2px 5px rgba(0, 0, 0, 0.2);
}

.header-container {
    max-width: 1200px;
    margin: 0 auto;
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 0 1.5rem;
}

.logo {
    font-size: 2.2rem;
    font-weight: bold;
    color: var(--secondary-color);
    text-transform: uppercase;
    letter-spacing: 1px;
    transition: color 0.3s ease;
}

.logo:hover {
    color: var(--light-text-color);
}

.main-nav .nav-list {
    display: flex;
    gap: 1.8rem;
}

.main-nav .nav-list a {
    color: var(--light-text-color);
    font-weight: 500;
    font-size: 1rem;
    padding: 0.5rem 0;
    position: relative;
}

.main-nav .nav-list a::after {
    content: '';
    position: absolute;
    left: 0;
    bottom: 0;
    width: 0;
    height: 2px;
    background-color: var(--secondary-color);
    transition: width 0.3s ease;
}

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

.hamburger-menu {
    display: none;
    flex-direction: column;
    justify-content: space-around;
    width: 30px;
    height: 25px;
    background: transparent;
    border: none;
    cursor: pointer;
    padding: 0;
    z-index: 1000;
}

.hamburger-menu .bar {
    width: 100%;
    height: 3px;
    background-color: var(--secondary-color);
    transition: all 0.3s ease;
}

/* Footer */
.site-footer {
    background-color: var(--dark-bg);
    color: var(--light-text-color);
    padding: 3rem 0;
    text-align: center;
    position: relative;
}

.footer-container {
    max-width: 1200px;
    margin: 0 auto;
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: 2rem;
    padding: 0 1.5rem;
    text-align: left;
}

.footer-column h3 {
    color: var(--secondary-color);
    font-size: 1.2rem;
    margin-bottom: 1rem;
}

.footer-column p,
.footer-column a {
    color: #bbb;
    font-size: 0.95rem;
    line-height: 1.8;
}

.footer-column a:hover {
    color: var(--secondary-color);
}

.logo-footer {
    font-size: 1.8rem;
    font-weight: bold;
    color: var(--secondary-color);
    text-transform: uppercase;
    letter-spacing: 1px;
    margin-bottom: 1rem;
    display: block;
}

.footer-nav li {
    margin-bottom: 0.5rem;
}

.copyright {
    margin-top: 2rem;
    font-size: 0.85rem;
    color: #888;
    text-align: center;
    grid-column: 1 / -1; /* Spans all columns */
}

.back-to-top {
    display: none; /* Hidden by default */
    position: fixed;
    bottom: 20px;
    right: 20px;
    background-color: var(--secondary-color);
    color: var(--primary-color);
    border: none;
    border-radius: 50%;
    width: 50px;
    height: 50px;
    font-size: 1.5rem;
    cursor: pointer;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.2);
    z-index: 999;
    transition: background-color 0.3s ease, transform 0.3s ease;
}

.back-to-top:hover {
    background-color: #e0b800;
    transform: translateY(-3px);
}

/* Responsive */
@media (max-width: 768px) {
    .header-container {
        padding: 0 1rem;
    }

    .main-nav {
        display: none;
        flex-direction: column;
        position: absolute;
        top: 60px; /* Adjust based on header height */
        left: 0;
        width: 100%;
        background-color: var(--primary-color);
        box-shadow: 0 2px 5px rgba(0, 0, 0, 0.2);
        z-index: 999;
        padding-bottom: 1rem;
    }

    .main-nav.active {
        display: flex;
    }

    .main-nav .nav-list {
        flex-direction: column;
        align-items: center;
        gap: 0.5rem;
    }

    .main-nav .nav-list a {
        padding: 0.8rem 1rem;
        width: 100%;
        text-align: center;
    }

    .main-nav .nav-list a::after {
        display: none;
    }

    .hamburger-menu {
        display: flex;
    }

    .hamburger-menu.active .bar:nth-child(1) {
        transform: translateY(11px) rotate(45deg);
    }

    .hamburger-menu.active .bar:nth-child(2) {
        opacity: 0;
    }

    .hamburger-menu.active .bar:nth-child(3) {
        transform: translateY(-11px) rotate(-45deg);
    }

    .footer-container {
        grid-template-columns: 1fr;
        text-align: center;
    }

    .footer-column {
        margin-bottom: 1.5rem;
    }

    .logo-footer {
        margin-left: auto;
        margin-right: auto;
    }

    .copyright {
        margin-top: 1rem;
    }

    .back-to-top {
        bottom: 15px;
        right: 15px;
        width: 45px;
        height: 45px;
        font-size: 1.3rem;
    }
}