:root{--blue:#075ee8;--navy:#05275d;--ink:#071c43;--muted:#5e6b82;--line:#e5ebf4;--bg:#f6f9fd;--radius:16px;--shadow:0 8px 24px rgba(16,48,95,.08)}*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;color:var(--ink);font-family:Inter,"Segoe UI",Arial,sans-serif;background:#fff;line-height:1.6}a{color:inherit;text-decoration:none}img{max-width:100%;height:auto}.site-header{position:sticky;top:0;z-index:50;background:rgba(255,255,255,.96);border-bottom:1px solid var(--line);backdrop-filter:blur(10px)}.header-inner{height:72px;max-width:1440px;margin:auto;padding:0 32px;display:flex;align-items:center;gap:30px}.brand img,.custom-logo{display:block;max-height:54px;width:auto}.main-nav{margin-left:auto}.main-nav ul{display:flex;align-items:center;gap:32px;list-style:none;margin:0;padding:0}.main-nav a{font-size:13px;font-weight:800}.main-nav a:hover{color:var(--blue)}.header-actions{display:flex;gap:12px;align-items:center}.search-link{font-size:26px}.menu-toggle{display:none;border:0;background:none;font-size:24px}.btn{display:inline-flex;align-items:center;justify-content:center;background:var(--blue);color:#fff!important;padding:13px 22px;border-radius:9px;font-weight:800;box-shadow:0 7px 18px rgba(7,94,232,.2)}.btn.small{padding:9px 16px;font-size:13px}.btn.secondary{background:#fff;color:var(--blue)!important;border:1px solid var(--line)}.btn.white{background:#fff;color:var(--navy)!important}.hero{max-width:1360px;margin:auto;min-height:390px;padding:55px 55px 30px;display:grid;grid-template-columns:1.1fr .9fr;align-items:center;background:linear-gradient(110deg,#fff 45%,#eef6ff)}.hero h1{font-size:56px;line-height:1;margin:0 0 15px;letter-spacing:-2px}.hero h2{font-size:22px;color:var(--blue);margin:0 0 18px}.hero p{max-width:470px;font-size:17px}.hero-actions{display:flex;gap:14px;margin-top:28px}.physics-art{height:290px;position:relative;font-size:100px;display:flex;align-items:center;justify-content:center;gap:25px;color:var(--blue)}.physics-art .magnet{font-size:90px}.physics-art .pendulum{font-size:50px;color:#253a55}.quick-grid{max-width:1280px;margin:0 auto 30px;padding:0 30px;display:grid;grid-template-columns:repeat(6,1fr);gap:16px}.quick-card{padding:24px 15px;text-align:center;border:1px solid var(--line);border-radius:12px;box-shadow:var(--shadow);background:#fff}.quick-card>div{font-size:38px}.quick-card h3{font-size:14px;margin:10px 0 4px}.quick-card p{font-size:12px;color:var(--muted);margin:0}.hatquiz-panel{max-width:1280px;margin:30px auto;padding:28px 35px;border-radius:14px;background:linear-gradient(120deg,#06285d,#00489d);color:#fff;display:grid;grid-template-columns:1.3fr repeat(4,1fr);gap:14px}.hatquiz-intro h2{font-size:34px;margin:0}.hatquiz-intro h3{margin:0 0 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a:hover{color:var(--blue)}.study-links{color:var(--blue);font-weight:700;font-size:13px}.explore{max-width:1280px;margin:40px auto;padding:28px 30px;background:#f6faff;border-radius:16px}.explore h2{margin-bottom:0}.explore>p{margin-top:0;color:var(--muted)}.posts-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:20px}.post-card{background:#fff;border:1px solid var(--line);border-radius:12px;overflow:hidden}.post-card img{width:100%;aspect-ratio:16/9;object-fit:cover}.post-card h2,.post-card h3,.post-card p,.post-card span{margin-left:16px;margin-right:16px}.post-card h3{font-size:17px}.post-card p{font-size:14px;color:var(--muted)}.post-card span{display:block;color:var(--blue);font-weight:700;margin-bottom:16px}.article-shell{max-width:1180px;margin:0 auto;padding:34px 30px 70px}.breadcrumbs{font-size:14px;color:#65748d;display:flex;gap:11px;flex-wrap:wrap;margin:0 0 20px}.breadcrumbs a:hover{color:var(--blue)}.article-header h1{font-size:42px;line-height:1.18;letter-spacing:-.8px;margin:0 0 28px}.article-content{font-size:17px;color:#17243a}.article-content>*{max-width:100%}.article-content h2{font-size:28px;color:var(--navy);margin-top:42px}.article-content h3{font-size:22px}.article-content p{margin:0 0 1.15em}.article-content img{border-radius:10px}.article-content pre,.article-content code{max-width:100%;overflow:auto}.article-content iframe{max-width:100%}.article-content .alignwide{width:min(1320px,calc(100vw - 40px));max-width:none;margin-left:50%;transform:translateX(-50%)}.article-content .alignfull{width:100vw;max-width:none;margin-left:50%;transform:translateX(-50%)}.fullwidth-shell{max-width:none;margin:0;padding:0}.fullwidth-shell>*{max-width:none}
.listing{max-width:1280px;margin:auto;padding:50px 30px}.empty{text-align:center;padding:100px 20px}.empty h1{font-size:80px;margin:0}.site-footer{background:linear-gradient(110deg,#06295e,#001c45);color:#fff;padding:42px 30px 20px}.footer-grid{max-width:1280px;margin:auto;display:grid;grid-template-columns:2fr 1fr 1fr 1fr;gap:50px}.footer-logo{max-width:150px;background:#fff;border-radius:6px;padding:4px}.footer-grid p{font-size:13px;opacity:.8;max-width:280px}.footer-grid h4{margin:0 0 10px}.footer-grid a{display:block;font-size:13px;opacity:.85;margin:5px 0}.copyright{text-align:center;opacity:.65;font-size:12px;margin-top:28px}.mobile-bottom{display:none}
@media(max-width:900px){body{padding-bottom:64px}.header-inner{height:62px;padding:0 16px}.brand img,.custom-logo{max-height:42px;max-width:120px}.menu-toggle{display:block;margin-left:auto}.main-nav{display:none;position:absolute;top:62px;left:0;right:0;background:#fff;border-bottom:1px solid var(--line);padding:16px}.main-nav.open{display:block}.main-nav ul{display:block}.main-nav li{padding:10px}.header-actions .btn{display:none}.hero{display:block;padding:35px 20px;text-align:center}.hero h1{font-size:34px}.hero h2{font-size:15px}.hero p{font-size:14px;margin:auto}.physics-art{height:160px;font-size:60px}.physics-art .magnet{font-size:55px}.physics-art .pendulum{font-size:30px}.hero-actions{display:grid}.quick-grid{grid-template-columns:repeat(3,1fr);padding:0 16px;gap:9px}.quick-card{padding:16px 7px}.quick-card>div{font-size:28px}.quick-card p{display:none}.hatquiz-panel{margin:20px 16px;padding:22px;display:grid;grid-template-columns:repeat(4,1fr);gap:8px;text-align:center}.hatquiz-intro{grid-column:1/-1}.hatquiz-intro h2{font-size:27px}.feature{padding:10px 5px}.feature>b{font-size:25px}.feature h3{font-size:9px}.feature p{display:none}.curriculum{padding:0 16px}.grade-tabs button{padding:8px 14px}.grade-panel ol{columns:1}.posts-grid{grid-template-columns:repeat(2,1fr)}.article-shell{padding:24px 18px 50px}.article-header h1{font-size:30px}.article-content{font-size:16px}.footer-grid{grid-template-columns:1fr 1fr}.mobile-bottom{position:fixed;z-index:60;bottom:0;left:0;right:0;height:64px;background:#fff;border-top:1px solid var(--line);display:grid;grid-template-columns:repeat(5,1fr);align-items:center;text-align:center}.mobile-bottom a{font-size:18px;color:#355071}.mobile-bottom span{display:block;font-size:9px}.hatquiz-mobile{color:var(--blue)!important;font-size:26px!important}}
@media(max-width:560px){.posts-grid{grid-template-columns:1fr}.footer-grid{grid-template-columns:1fr}.quick-card h3{font-size:11px}.article-content .alignwide{width:100%;margin-left:0;transform:none}}

/* ===== Content Hub / Trang lọc ===== */
.hvl-hub{max-width:1240px;margin:0 auto;padding:48px 22px 70px}.hub-heading{margin-bottom:24px}.hub-heading h1{margin:4px 0 6px;color:#0b2454;font-size:clamp(28px,4vw,42px)}.hub-heading p{margin:0;color:#6d7890}.hub-kicker{font-weight:800!important;letter-spacing:.12em;color:#0b63e5!important;font-size:13px}.filter-panel{border:1px solid #dfe7f2;border-radius:20px;padding:24px;background:#fff;box-shadow:0 12px 35px rgba(11,36,84,.05)}.filter-title{font-size:13px;font-weight:900;letter-spacing:.13em;color:#0b63e5;margin-bottom:16px}.topic-tabs{display:flex;gap:10px;flex-wrap:wrap;padding-bottom:20px;border-bottom:1px solid #e8edf5}.topic-tab{display:inline-flex;gap:7px;align-items:center;min-height:44px;padding:0 17px;border:1px solid #dce4ef;border-radius:12px;color:#35435d;font-weight:800;background:#fff;text-decoration:none;transition:.2s}.topic-tab span{color:#9aa6b9}.topic-tab:hover{border-color:#80b2f4;color:#075ccf}.topic-tab.active{background:#075fcf;color:#fff;border-color:#075fcf;box-shadow:0 7px 18px rgba(7,95,207,.18)}.topic-tab.active span{color:#dceaff}.filter-tools{display:grid;grid-template-columns:1fr auto;gap:12px;margin:16px 0 20px}
.select-tabs{display:block;padding-bottom:14px}.topic-select-wrap{max-width:340px}.topic-select{width:100%;border:0;outline:0;background:transparent;font:inherit;font-weight:700;color:#35435d;padding:0 4px}.select-wrap,.search-wrap{height:48px;border:1px solid #d9e2ef;border-radius:13px;display:flex;align-items:center;background:#fff}.select-wrap{padding:0 12px}.select-wrap select{width:100%;border:0;outline:0;background:transparent;font:inherit;font-weight:700;color:#35435d}.filter-icon{font-size:11px;color:#075fcf;margin-right:7px}.search-wrap{padding:0 16px;gap:10px}.search-wrap span{font-size:24px;color:#075fcf}.search-wrap input{width:100%;border:0;outline:0;font:inherit;color:#26334b}.filter-submit{border:0;border-radius:12px;padding:0 24px;background:#075fcf;color:#fff;font-weight:800;cursor:pointer}.hub-table-wrap{overflow:auto;border-radius:15px;border:1px solid #e1e7f0}.hub-table{width:100%;border-collapse:collapse;min-width:1000px}.hub-table th{background:#082e68;color:#fff;text-align:left;padding:16px 18px;font-size:12px;letter-spacing:.08em}.hub-table th:first-child{width:70px}.hub-table td{padding:16px 18px;border-bottom:1px solid #e6ebf3;border-right:1px solid #eef2f7;color:#26334b;vertical-align:middle}.hub-table tr:last-child td{border-bottom:0}.hub-table tbody tr:hover{background:#f7faff}.row-no{font-family:monospace;color:#71809a}.post-name{font-weight:750;color:#162a4e;text-decoration:none}.post-name:hover,.excerpt-link:hover{color:#075fcf}.excerpt-link{display:block;max-width:360px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis;color:#4e5e78;text-decoration:none}.type-pill{display:inline-flex;align-items:center;padding:6px 11px;border-radius:999px;background:#eaf3ff;border:1px solid #b8d5ff;color:#075fcf;font-size:12px;font-weight:800}.type-pill.neutral{background:#f3f5f8;border-color:#dfe4eb;color:#68758b}.hub-table em{color:#71809a;font-weight:650}.empty-state{text-align:center!important;padding:44px!important;color:#71809a!important}.hub-pagination{display:flex;justify-content:center;gap:7px;margin-top:20px}.hub-pagination a{width:38px;height:38px;border:1px solid #dce4ef;border-radius:10px;display:grid;place-items:center;text-decoration:none;color:#355071;font-weight:800}.hub-pagination a.active{background:#075fcf;color:#fff;border-color:#075fcf}
@media(max-width:900px){.hvl-hub{padding:28px 14px 88px}.filter-panel{padding:15px;border-radius:16px}.topic-tabs{flex-wrap:wrap;padding-bottom:14px}.topic-tab{min-height:40px;padding:0 13px}.select-tabs{overflow-x:visible}.topic-select-wrap{max-width:none}.filter-tools{grid-template-columns:1fr}.filter-submit{height:46px}.hub-table-wrap{border:0;overflow:visible}.hub-table{min-width:0}.hub-table thead{display:none}.hub-table,.hub-table tbody,.hub-table tr,.hub-table td{display:block;width:100%}.hub-table tr{border:1px solid #e1e7f0;border-radius:14px;margin-bottom:12px;padding:10px 12px;background:#fff;box-shadow:0 5px 18px rgba(11,36,84,.04)}.hub-table td{border:0;padding:6px 0;display:grid;grid-template-columns:88px 1fr;gap:10px}.hub-table td:before{content:attr(data-label);font-size:11px;text-transform:uppercase;letter-spacing:.05em;color:#8b98ac;font-weight:800}.excerpt-link{max-width:none;white-space:normal}.hub-table td:first-child{display:none}}
/* v1.2 content library */
.chapter-tabs{display:flex;gap:8px;flex-wrap:wrap;padding:14px 0 2px}.chapter-tab{padding:8px 12px;border-radius:10px;background:#f5f8fd;border:1px solid #dfe7f2;color:#3d4f6d;text-decoration:none;font-size:13px;font-weight:750}.chapter-tab:hover,.chapter-tab.active{background:#eaf3ff;border-color:#9cc6ff;color:#075fcf}.result-count{margin:-5px 0 12px;color:#74829a;font-size:13px}.result-count strong{color:#0b2454}.excerpt-link.external{color:#1267e8;font-family:ui-monospace,SFMono-Regular,Menlo,monospace}.grade-tabs{margin-bottom:0}
@media(max-width:900px){.chapter-tab{padding:7px 11px;font-size:12px}}

.ui-icon{width:1.25em;height:1.25em;display:inline-block;vertical-align:-.18em;fill:none;stroke:currentColor;stroke-width:1.8;stroke-linecap:round;stroke-linejoin:round}.menu-toggle .ui-icon,.search-link .ui-icon{width:24px;height:24px}.mobile-bottom .ui-icon{display:block;margin:0 auto 2px;width:21px;height:21px}.hatquiz-mobile .ui-icon{width:27px;height:27px;fill:currentColor;stroke:none}.article-meta{display:flex;align-items:center;gap:7px;margin:-16px 0 26px;color:var(--muted);font-size:14px}.article-meta .ui-icon{width:18px;height:18px}