:root {
    --vn-red: #e62117;
    --vn-blue: #003466;
    --vn-correct-border: #008a3c;
    --vn-correct-bg: #e6f9ed;
    --vn-wrong-border: #e62117;
    --vn-wrong-bg: #fff1f0;
    --bar-gray: #f2f2f2;
    --border-color: #eee;
}
.text-center{ text-align: center; }
* { box-sizing: border-box; -webkit-tap-highlight-color: transparent; }
body { font-family: 'Roboto', sans-serif; margin: 0; background: #fff; color: #222; line-height: 1.6; overflow-x: hidden; }
/* --- HEADER & RESPONSIVE MENU --- */
header { border-bottom: 2px solid var(--vn-red); /*position: sticky; top: 0;*/ background: #fff; z-index: 1000; box-shadow: 0 2px 10px rgba(0,0,0,0.05); }
.nav-inner { max-width: 1200px; margin: 0 auto; display: flex; justify-content: space-between; align-items: center; padding: 10px 20px; height: 64px; }
.logo { font-family: 'Merriweather', serif; color: var(--vn-red); font-size: 1.6rem; text-decoration: none; font-weight: bold; z-index: 1001; }
.menu-toggle { display: none; font-size: 1.8rem; cursor: pointer; color: var(--vn-blue); z-index: 1001; }
.nav-menu { display: flex; list-style: none; margin: 0; padding: 0; }
.nav-menu > li { position: relative; }
.nav-menu > li > a { padding: 20px 15px; display: block; text-decoration: none; color: var(--vn-blue); font-weight: 700; font-size: 0.85rem; text-transform: uppercase; }
/* Dropdown Desktop */
.dropdown {
    position: absolute; top: 100%; left: 0; background: #fff; min-width: 220px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.1); list-style: none; padding: 10px 0;
    border-top: 2px solid var(--vn-red); opacity: 0; visibility: hidden;
    transform: translateY(10px); transition: 0.3s; z-index: 9999;
}
.dropdown li a { padding: 10px 20px; display: block; text-decoration: none; color: #333; font-size: 0.9rem; border-bottom: 1px solid #f9f9f9; }
.dropdown li a:hover { background: #f8f8f8; color: var(--vn-red); }
.nav-menu > li:hover .dropdown { opacity: 1; visibility: visible; transform: translateY(0); }
.nav-menu > li:hover > a { color: var(--vn-red); }
/* --- LAYOUT 2 CỘT (STICKY BOUNDARY) --- */
.sticky-wrapper { max-width: 1200px; margin: 30px auto; display: grid; grid-template-columns: 1fr 320px; gap: 40px; padding: 0 20px; align-items: start; }
.main-content { min-width: 0; }
.sidebar { position: sticky; top: 84px; padding-bottom: 20px; }
/* --- BÀI VIẾT & QUIZ --- */
.breadcrumb { font-size: 0.75rem; color: var(--vn-red); font-weight: 700; text-transform: uppercase; margin-bottom: 10px; }
h1 { font-family: 'Merriweather', serif; font-size: 2.2rem; line-height: 1.3; margin: 0 0 20px 0; }
.sapo { font-size: 1.1rem; color: #555; border-left: 4px solid #ddd; padding-left: 20px; margin-bottom: 30px; font-weight: 300; }
.quiz-item { border: 1px solid var(--border-color); border-radius: 8px; margin-bottom: 10px; overflow: hidden; }
.quiz-header { padding: 15px 20px; background: #f8f9fa; font-weight: bold; font-size: 1.1rem; border-bottom: 1px solid var(--border-color); }
.quiz-body { padding: 10px 20px; }
.option {
    position: relative; padding: 5px 10px 5px 10px; border: 1px solid #ddd; margin-bottom: 10px; 
    border-radius: 5px; cursor: pointer; display: flex; justify-content: space-between; overflow: hidden;
    z-index: 1; font-weight: 500; transition: background 0.2s;
}
.option::before { 
    content: ""; position: absolute; top: 0; left: 0; height: 100%; width: 0; 
    background: var(--bar-gray); z-index: -1; transition: width 0.8s cubic-bezier(0.1, 0.5, 0.5, 1); 
}
.option.active::before { width: var(--p); }
.option.correct { border-color: var(--vn-correct-border) !important; background: var(--vn-correct-bg) !important; color: var(--vn-correct-border) !important; font-weight: bold; }
.option.wrong { border-color: var(--vn-wrong-border) !important; background: var(--vn-wrong-bg) !important; color: var(--vn-wrong-border) !important; font-weight: bold; }

.p-text { display: none; font-weight: bold; position: absolute; right: 15px; color: #666; }
.option.active .p-text { display: block; }
.explanation { display: none; padding: 15px; background: #fffde7; border: 1px dashed #fbc02d; margin-top: 15px; font-size: 0.95rem; border-radius: 4px; }
/* --- SIDEBAR WIDGETS --- */
.box-title { border-bottom: 2px solid var(--vn-blue); padding-bottom: 5px; font-weight: bold; margin-bottom: 20px; display: block; color: var(--vn-blue); font-size: 1rem; }
.card-link { display: flex; gap: 12px; margin-bottom: 20px; text-decoration: none; color: inherit; }
.card-link img { width: 100px; height: 65px; object-fit: cover; border-radius: 4px; flex-shrink: 0; }
.card-link h4 { margin: 0; font-size: 0.85rem; line-height: 1.4; transition: 0.2s; }
.card-link:hover h4 { color: var(--vn-red); }
/* --- BOTTOM SECTION (OUTSIDE STICKY WRAPPER) --- */
.bottom-section { background: #f9f9f9; border-top: 1px solid var(--border-color); padding: 50px 0; }
.bottom-container { max-width: 1200px; margin: 0 auto; padding: 0 20px; }
.bottom-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 20px; margin-top: 20px; }
.bottom-card { text-decoration: none; color: inherit; background: #fff; padding: 10px; border-radius: 8px; transition: 0.3s; }
.bottom-card:hover { transform: translateY(-5px); box-shadow: 0 5px 15px rgba(0,0,0,0.1); }
.bottom-card img { width: 100%; height: 140px; object-fit: cover; border-radius: 4px; }
.bottom-card h4 { margin: 12px 0 0; font-size: 0.9rem; line-height: 1.4; font-weight: 700; }
/* --- FOOTER --- */
footer { background: #1a1a1a; color: #999; padding: 50px 0 30px; }
.footer-inner { max-width: 1200px; margin: 0 auto; display: grid; grid-template-columns: 2fr 1fr 1fr; gap: 40px; padding: 0 20px; }
.footer-logo { font-family: 'Merriweather', serif; color: #fff; font-size: 1.5rem; margin-bottom: 15px; display: block; text-decoration: none; }
.footer-col h4 { color: #fff; text-transform: uppercase; font-size: 0.85rem; margin-bottom: 20px; border-left: 3px solid var(--vn-red); padding-left: 10px; }
.footer-col ul { list-style: none; padding: 0; }
.footer-col li { margin-bottom: 10px; font-size: 0.85rem; }
/* --- MOBILE MENU OVERLAY --- */
.overlay { display: none; position: fixed; top: 0; left: 0; width: 100%; height: 100%; background: rgba(0,0,0,0.5); z-index: 998; }
.overlay.active { display: block; }
/* --- RESPONSIVE SETTINGS --- */
@media (max-width: 900px) {
    .menu-toggle { display: block; }
    .nav-menu {
position: fixed; top: 0; right: -100%; width: 280px; height: 100vh;
background: #fff; flex-direction: column; transition: 0.4s;
padding: 80px 20px 20px; z-index: 999; overflow-y: auto;
    }
    .nav-menu.active { right: 0; }
    .nav-menu > li { border-bottom: 1px solid #eee; }
    .nav-menu > li > a { padding: 15px 0; font-size: 1rem; }
    .dropdown { position: static; opacity: 1; visibility: visible; display: none; box-shadow: none; border: none; background: #f9f9f9; transform: none; padding-left: 15px; }
    .nav-menu li.open .dropdown { display: block; }
    .nav-menu li.has-child > a::after { content: " ▾"; }
    .sticky-wrapper { grid-template-columns: 1fr; margin: 15px auto; }
    .sidebar { display: none; }
    .bottom-grid { grid-template-columns: 1fr 1fr; }
    h1 { font-size: 1.7rem; }
    .footer-inner { grid-template-columns: 1fr; }
}
.logo img{width: 120px;}
@media (max-width: 768px) {
	.logo img{width: 200px;}
	.qhvn{display:none !important;}
}
.main-content a{
    text-decoration: none;
    color: #2552a3;
}
.container-button-puzzle {
    text-align: center;
    margin: 10px 0 10px 0;
    padding: 0 15px;
}
.btn-puzzle-more {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    background: #ffffff;
    color: #0ea3f0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    font-size: 15px;
    font-weight: 700;
    text-decoration: none;
    letter-spacing: 0.5px;
    padding: 14px 32px;
    border-radius: 50px;
    border: 2px solid #0ea3f0;
    box-shadow: 0 4px 14px rgba(14, 163, 240, 0.15);
    position: relative;
    transition: all 0.3s cubic-bezier(0.25, 0.8, 0.25, 1);
    cursor: pointer;
}
.btn-puzzle-more .icon-left {
    margin-right: 10px;
    font-size: 16px;
}
.btn-puzzle-more .icon-right {
    margin-left: 8px;
    font-size: 13px;
    transition: transform 0.3s ease;
}
@media (hover: hover) {
    .btn-puzzle-more:hover {
        background: #0ea3f0;
        color: #ffffff;
        box-shadow: 0 6px 20px rgba(14, 163, 240, 0.4);
        transform: translateY(-3px);
    }
    .btn-puzzle-more:hover .icon-right {
        transform: translateX(4px);
    }
}
.btn-puzzle-more:active {
    transform: translateY(1px);
    box-shadow: 0 2px 8px rgba(14, 163, 240, 0.2);
}
@media (max-width: 480px) {
    .btn-puzzle-more {
        display: flex;
        width: 100%;
        box-sizing: border-box;
        padding: 15px 20px;
        font-size: 16px;
    }
}
.footer-col a{
	color: #999;
	text-decoration: none;
}
.footer-col a:hover{
	text-decoration: underline;
}