:root {
    --primary-color: #C63A32;
    --secondary-color: #0F3047;
    --bg-body: #F9FAFB;
    --bg-card: #FFFFFF;
    --text-main: #111827;
    --text-sub: #6B7280;
    --border-color: #E5E7EB;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
}
body.dark-mode {
    --primary-color: #EF4444;
    --secondary-color: #38BDF8;
    --bg-body: #0F172A;
    --bg-card: #1E293B;
    --text-main: #F1F5F9;
    --text-sub: #94A3B8;
    --border-color: #334155;
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.5);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.5);
}
* { box-sizing: border-box; margin: 0; padding: 0; }
body { font-family: 'Be Vietnam Pro', sans-serif; background: var(--bg-body); color: var(--text-main); line-height: 1.6; font-size: 16px; transition: 0.3s; }
a { text-decoration: none; color: inherit; }
.site-header { background: var(--bg-card); border-bottom: 1px solid var(--border-color); padding: 0 20px; position: sticky; top: 0; z-index: 100; transition: 0.3s; }
.header-inner { max-width: 1200px; margin: 0 auto; height: 70px; display: flex; align-items: center; justify-content: space-between; }
.brand { display: flex; align-items: center; gap: 12px; font-weight: 800; font-size: 26px; color: var(--secondary-color); }
.brand img { height: 45px; width: auto; }
.theme-btn { background: transparent; border: 1px solid var(--border-color); width: 44px; height: 44px; border-radius: 12px; cursor: pointer; display: flex; align-items: center; justify-content: center; transition: 0.2s; }
.theme-btn:hover { background: var(--border-color); }
.theme-btn img { width: 22px; height: 22px; }
.coursebar { background: var(--bg-card); border-bottom: 1px solid var(--border-color); padding: 16px 0; margin-bottom: 30px; transition: 0.3s; }
.coursebar-inner { max-width: 1200px; margin: 0 auto; padding: 0 20px; display: flex; align-items: center; justify-content: space-between; gap: 16px; flex-wrap: wrap; }
.course-meta { min-width: 0; }
.course-title-wrap { display: flex; align-items: center; gap: 12px; }
.back-btn-inline { display: block; transition: transform 0.2s ease; line-height: 0; }
.back-btn-inline:hover { transform: translateX(-4px); }
.back-btn-inline img { width: 28px; height: 28px; display: block; }
.course-title { font-size: 1.25rem; font-weight: 700; color: var(--text-main); }
.course-sub { font-size: 0.9rem; color: var(--text-sub); margin-top: 0; }
.course-actions { display: flex; align-items: center; gap: 12px; flex-shrink: 0; }
.social-btn { width: 38px; height: 38px; display: grid; place-items: center; border-radius: 50%; border: 1px solid var(--border-color); background: var(--bg-card); box-shadow: var(--shadow-sm); transition: 0.2s; }
.social-btn img { width: 20px; height: 20px; object-fit: contain; }
.social-btn:hover { transform: translateY(-2px); border-color: var(--secondary-color); }
.layout-grid { max-width: 1200px; margin: 40px auto; padding: 0 20px; display: grid; grid-template-columns: 2.5fr 1fr; gap: 30px; }
.box-panel { background: var(--bg-card); border: 1px solid var(--border-color); border-radius: 16px; padding: 30px; box-shadow: var(--shadow-sm); transition: 0.3s; }
.section-head { margin-bottom: 25px; }
.head-title { font-size: 22px; font-weight: 700; color: var(--text-main); }
.subjects-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 20px; }
.subject-card-home { border: 1px solid var(--border-color); border-radius: 16px; padding: 25px; display: flex; flex-direction: column; align-items: center; text-align: center; transition: 0.2s; background: var(--bg-card); position: relative; overflow: hidden; }
.subject-card-home:hover { transform: translateY(-5px); box-shadow: var(--shadow-md); }
.home-blue { border-top: 4px solid #3B82F6; }
.home-blue:hover { background: linear-gradient(to bottom, #EFF6FF, var(--bg-card)); border-color: #3B82F6; }
.home-purple { border-top: 4px solid #8B5CF6; }
.home-purple:hover { background: linear-gradient(to bottom, #F5F3FF, var(--bg-card)); border-color: #8B5CF6; }
.home-orange { border-top: 4px solid #F97316; }
.home-orange:hover { background: linear-gradient(to bottom, #FFF7ED, var(--bg-card)); border-color: #F97316; }
body.dark-mode .home-blue:hover { background: linear-gradient(to bottom, rgba(59, 130, 246, 0.1), var(--bg-card)); }
body.dark-mode .home-purple:hover { background: linear-gradient(to bottom, rgba(139, 92, 246, 0.1), var(--bg-card)); }
body.dark-mode .home-orange:hover { background: linear-gradient(to bottom, rgba(249, 115, 22, 0.1), var(--bg-card)); }
.sub-icon { width: 64px; height: 64px; margin-bottom: 15px; object-fit: contain; background: #FFFFFF; border: 1px solid var(--border-color); border-radius: 18px; padding: 10px; box-shadow: 0 4px 10px rgba(0,0,0,0.05); transition: 0.3s; }
.subject-card-home:hover .sub-icon { transform: scale(1.1) rotate(-5deg); box-shadow: 0 8px 15px rgba(0,0,0,0.1); }
body.dark-mode .sub-icon { background: rgba(255, 255, 255, 0.05); border-color: var(--border-color); box-shadow: none; }
.sub-name { font-weight: 700; font-size: 18px; color: var(--text-main); }
.tools-stack { display: flex; flex-direction: column; gap: 20px; }
.tool-card { display: flex; align-items: center; gap: 20px; padding: 20px; border: 1px solid var(--border-color); border-radius: 16px; background: var(--bg-card); transition: 0.2s; box-shadow: var(--shadow-sm); }
.tool-card:hover { transform: translateX(-5px); border-color: var(--secondary-color); }
.tool-icon { width: 54px; height: 54px; border-radius: 14px; display: flex; align-items: center; justify-content: center; flex-shrink: 0; transition: 0.2s; }
.tool-icon img { width: 32px; height: 32px; object-fit: contain; }
.tool-card:hover .tool-icon { transform: scale(1.1); }
.tool-text-main { font-weight: 700; font-size: 22px; color: var(--text-main); }
.exam-grid-layout { max-width: 1200px; margin: 0 auto 40px; padding: 0 20px; display: grid; grid-template-columns: repeat(3, 1fr); gap: 25px; align-items: start; }
.subject-accordion { background: var(--bg-card); border: 1px solid var(--border-color); border-radius: 12px; overflow: hidden; transition: 0.3s; box-shadow: var(--shadow-sm); }
.subject-accordion:hover { box-shadow: var(--shadow-md); }
.accordion-header { padding: 20px; display: flex; align-items: center; gap: 15px; cursor: pointer; user-select: none; position: relative; border-left: 5px solid transparent; }
.accordion-header:hover { background: rgba(0,0,0,0.02); }
.acc-icon { width: 52px; height: 52px; object-fit: contain; background: #FFFFFF; border: 1px solid var(--border-color); border-radius: 14px; padding: 8px; box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.05); flex-shrink: 0; transition: transform 0.2s; }
.subject-accordion:hover .acc-icon { transform: scale(1.05); border-color: var(--secondary-color); }
body.dark-mode .acc-icon { background: rgba(255, 255, 255, 0.05); border-color: var(--border-color); box-shadow: none; }
.acc-title { font-weight: 700; font-size: 18px; flex: 1; color: var(--text-main); }
.acc-arrow { transition: transform 0.4s ease; color: var(--text-sub); }
.accordion-body { display: grid; grid-template-rows: 0fr; transition: grid-template-rows 0.5s ease-out; background: var(--bg-card); border-top: 1px solid transparent; }
.acc-inner { overflow: hidden; }
.subject-accordion:hover .accordion-body, .subject-accordion.active .accordion-body { grid-template-rows: 1fr; border-top-color: var(--border-color); }
.subject-accordion:hover .acc-arrow, .subject-accordion.active .acc-arrow { transform: rotate(180deg); }
.hp-link { display: block; padding: 12px 20px; color: var(--text-main); font-size: 15px; border-bottom: 1px solid var(--border-color); transition: 0.2s; }
.hp-link:hover { background: var(--bg-body); color: var(--primary-color); padding-left: 25px; }
.hp-link:last-child { border-bottom: none; }
.border-blue { border-left-color: #3B82F6; }
.border-purple { border-left-color: #8B5CF6; }
.border-cyan { border-left-color: #06B6D4; }
.border-indigo { border-left-color: #6366F1; }
.border-orange { border-left-color: #F97316; }
.border-green { border-left-color: #10B981; }
.bg-blue { background: #E0F2FE; color: #0284C7; }
.bg-orange { background: #FFF7ED; color: #EA580C; }
.search-bar-container { max-width: 700px; margin: 0 auto 40px; position: relative; }
.search-input { width: 100%; padding: 18px 25px; padding-left: 55px; border-radius: 12px; border: 1px solid var(--border-color); background: var(--bg-card); color: var(--text-main); font-family: inherit; font-size: 16px; outline: none; box-shadow: var(--shadow-sm); transition: 0.3s; }
.search-input:focus { border-color: var(--secondary-color); box-shadow: 0 0 0 4px rgba(15, 48, 71, 0.1); }
.search-icon { position: absolute; left: 20px; top: 50%; transform: translateY(-50%); color: var(--text-sub); font-size: 20px; }
.file-list { display: flex; flex-direction: column; }
.file-item { display: flex; align-items: center; justify-content: space-between; padding: 20px; border-bottom: 1px solid var(--border-color); background: var(--bg-card); transition: 0.3s; }
.file-item:last-child { border-bottom: none; }
.file-item:hover { background: var(--bg-body); }
.file-info { display: flex; align-items: center; gap: 20px; }
.file-icon { font-size: 28px; color: var(--secondary-color); }
.file-name { font-weight: 700; font-size: 16px; color: var(--text-main); }
.file-meta { font-size: 14px; color: var(--text-sub); margin-top: 4px; }
.btn-download { background: var(--bg-card); border: 1px solid var(--border-color); color: var(--text-main); padding: 10px 20px; border-radius: 8px; font-size: 14px; font-weight: 600; cursor: pointer; display: flex; align-items: center; gap: 8px; transition: 0.2s; }
.btn-download:hover { border-color: var(--secondary-color); color: var(--secondary-color); background: #F0F9FF; }
.msg-popup { position: fixed; bottom: 30px; left: 30px; width: 300px; background: #C63A32; color: #FFFFFF; border-radius: 8px; padding: 15px 20px; box-shadow: 0 10px 25px -5px rgba(198, 58, 50, 0.4); z-index: 9999; font-size: 14px; line-height: 1.5; opacity: 0; visibility: hidden; transform: translateY(10px); transition: all 0.5s cubic-bezier(0.19, 1, 0.22, 1); pointer-events: none; }
.msg-popup.active { opacity: 1; visibility: visible; transform: translateY(0); pointer-events: auto; }
.error-page { min-height: 80vh; display: flex; flex-direction: column; align-items: center; justify-content: center; padding: 40px 20px; text-align: center; }
.error-robot { width: 280px; height: auto; margin-bottom: 30px; transition: 0.3s; }
.error-robot:hover { transform: scale(1.05) rotate(2deg); }
.error-card { background: var(--bg-card); border: 1px solid var(--border-color); border-radius: 24px; padding: 40px; max-width: 550px; width: 100%; box-shadow: var(--shadow-md); position: relative; overflow: hidden; }
.error-card::before { content: ""; position: absolute; top: 0; left: 0; width: 100%; height: 6px; background: linear-gradient(90deg, var(--secondary-color), var(--primary-color)); }
.error-title { font-size: 42px; font-weight: 800; color: var(--primary-color); margin-bottom: 10px; line-height: 1.2; }
.error-desc { font-size: 16px; color: var(--text-main); margin-bottom: 30px; opacity: 0.9; }
.btn-error { display: inline-flex; align-items: center; justify-content: center; background: var(--secondary-color); color: #fff; padding: 14px 35px; border-radius: 50px; font-weight: 700; transition: 0.2s; box-shadow: 0 4px 10px rgba(0,0,0,0.1); }
.btn-error:hover { transform: translateY(-3px); filter: brightness(1.1); box-shadow: 0 8px 15px rgba(0,0,0,0.2); }
body.dark-mode .error-robot { filter: brightness(0.9); }
.site-footer { background: var(--bg-card); border-top: 1px solid var(--border-color); padding: 40px 20px; margin-top: 60px; display: flex; flex-direction: column; align-items: center; gap: 20px; text-align: center; }
.footer-socials { display: flex; align-items: center; gap: 15px; }
.footer-social-btn { width: 44px; height: 44px; border: 1px solid var(--border-color); border-radius: 50%; display: flex; align-items: center; justify-content: center; transition: 0.3s; background: var(--bg-body); }
.footer-social-btn img { width: 22px; height: 22px; object-fit: contain; }
.footer-social-btn:hover { border-color: var(--secondary-color); transform: translateY(-3px); box-shadow: var(--shadow-sm); }
.footer-copyright { color: var(--text-sub); font-size: 14px; font-weight: 500; }
@media (max-width: 900px) {
    .layout-grid { grid-template-columns: 1fr; }
    .exam-grid-layout { grid-template-columns: 1fr; }
    .coursebar-inner { flex-direction: column; align-items: flex-start; gap: 10px; }
    .course-actions { width: 100%; justify-content: flex-start; }
}
.coursebar{background:var(--bg-card);border-bottom:1px solid var(--border-color);padding:16px 0;margin-bottom:30px;transition:.3s}
.coursebar-inner{max-width:1420px;margin:0 auto;padding:0 20px;display:flex;align-items:center;justify-content:space-between;gap:16px;flex-wrap:wrap}
.course-meta{min-width:0}
.course-title-wrap{display:flex;align-items:center;gap:12px}
.back-btn-inline{display:block;transition:transform .2s ease;line-height:0}
.back-btn-inline:hover{transform:translateX(-4px)}
.back-btn-inline img{width:28px;height:28px;display:block}
.course-title{font-size:1.25rem;font-weight:700;color:var(--text-main)}
.course-sub{font-size:.9rem;color:var(--text-sub);margin-top:0}
.course-actions{display:flex;align-items:center;gap:12px;flex-shrink:0}
.social-btn{width:38px;height:38px;display:grid;place-items:center;border-radius:50%;border:1px solid var(--border-color);background:var(--bg-card);box-shadow:var(--shadow-sm);transition:.2s}
.social-btn img{width:20px;height:20px;object-fit:contain}
.social-btn:hover{transform:translateY(-2px);border-color:var(--secondary-color)}
/* Mobile Responsive căn giữa */
@media(max-width:1024px){
.coursebar-inner{flex-direction:column;justify-content:center;gap:15px}
.course-title-wrap{flex-direction:row;justify-content:center;width:100%;text-align:left}
.course-actions{justify-content:center;width:100%}
}
.user-account-box {
    display: inline-flex;
    align-items: center;
    margin-left: 15px;
}

.btn-ms-login {
    display: inline-flex;
    align-items: center;
    background-color: #2F2F2F;
    color: #fff !important;
    padding: 5px 10px;
    border-radius: 4px;
    text-decoration: none;
    font-size: 14px;
    font-weight: 500;
    transition: 0.2s;
    border: 1px solid transparent;
}

.btn-ms-login:hover {
    background-color: #0078D4;
    border-color: #0078D4;
}

.user-info-display {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 14px;
    color: #333;
}

.user-name-highlight {
    font-weight: bold;
    color: #C63A32;
}

.btn-logout {
    font-size: 12px;
    text-decoration: underline;
    cursor: pointer;
    color: #666;
}
.auth-block {
    display: flex;
    align-items: center;
    gap: 10px;
}

.nav-avatar-small {
    width: 32px;
    height: 32px;
    background-color: #b71c1c;
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: bold;
    font-size: 14px;
    text-decoration: none;
    text-transform: uppercase;
    border: 2px solid #fff;
    box-shadow: 0 2px 4px rgba(0,0,0,0.2);
}

.nav-username {
    font-size: 0.9rem;
    color: #333;
    font-weight: 500;
}

.d-none {
    display: none !important;
}