:root{--navy:#0B1F3A;--blue:#1565C0;--cyan:#00A6C7;--light:#F4F8FC;--green:#2E7D32;--red:#B3261E;--border:#D9E3EE;--text:#16202A}
*{box-sizing:border-box} body{margin:0;font-family:Inter,Arial,sans-serif;color:var(--text);background:#eef4fa;line-height:1.62} a{color:inherit;text-decoration:none}
.topbar{background:linear-gradient(135deg,var(--navy),#123d6b);color:#fff;padding:18px 0;box-shadow:0 4px 16px rgba(0,0,0,.14)} .wrap{width:min(1180px,92%);margin:auto}
.brand{display:flex;align-items:center;justify-content:space-between;gap:20px} .logo{font-weight:800;letter-spacing:.4px;font-size:1.2rem} .logo small{display:block;font-weight:500;opacity:.8;font-size:.78rem}
.hero{padding:44px 0 28px} .hero h1{font-size:clamp(2rem,5vw,3.6rem);margin:0;color:var(--navy);line-height:1.05} .hero p{max-width:760px;font-size:1.06rem;color:#425466}
.pills{display:flex;gap:10px;flex-wrap:wrap;margin-top:18px} .pill,.badge{display:inline-flex;align-items:center;gap:6px;padding:6px 11px;border-radius:999px;font-size:.82rem;font-weight:700}
.pill{background:#fff;border:1px solid var(--border)} .badge.basic{background:#E8F5E9;color:#1B5E20} .badge.medium{background:#FFF3CD;color:#7A5200} .badge.hard{background:#FDECEA;color:#8A1C16}
.grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:18px;padding:20px 0 50px} .card{background:#fff;border:1px solid var(--border);border-radius:18px;padding:20px;display:flex;flex-direction:column;min-height:305px;box-shadow:0 8px 24px rgba(11,31,58,.06)}
.card h3{color:var(--navy);margin:9px 0 6px;font-size:1.15rem} .meta{display:flex;justify-content:space-between;gap:8px;align-items:center;flex-wrap:wrap} .code{font-weight:900;color:var(--blue)}
.progress{height:8px;background:#e7edf4;border-radius:99px;overflow:hidden;margin:14px 0} .progress span{display:block;height:100%;background:linear-gradient(90deg,var(--blue),var(--cyan));border-radius:99px} .card p{color:#51606f;flex:1}
.actions{display:grid;grid-template-columns:1fr auto;gap:10px;margin-top:14px} .btn{display:inline-flex;justify-content:center;align-items:center;padding:10px 14px;border-radius:10px;font-weight:800;border:1px solid var(--blue)} .btn.primary{background:var(--blue);color:#fff} .btn.secondary{color:var(--blue);background:#fff}
.exercise{width:min(940px,92%);margin:30px auto 70px;background:#fff;border:1px solid var(--border);border-radius:22px;overflow:hidden;box-shadow:0 12px 32px rgba(11,31,58,.08)} .exercise-head{background:linear-gradient(135deg,var(--navy),#154e82);color:#fff;padding:30px} .exercise-head h1{margin:6px 0;font-size:clamp(1.65rem,4vw,2.4rem)} .exercise-body{padding:28px}
.section{margin:0 0 24px;padding:21px;border:1px solid var(--border);border-radius:14px;background:#fff} .section h2{margin:0 0 12px;color:var(--navy);font-size:1.2rem} .section.hint{background:#F7FBFF;border-left:5px solid var(--cyan)} .section.solution{background:#FBFCFE;border-left:5px solid var(--blue)} .section.mistakes{background:#FFF9F7;border-left:5px solid var(--red)}
.math{font-family:'Times New Roman',serif;text-align:center;font-size:1.12rem;padding:9px;background:#f7f9fc;border-radius:8px;margin:10px 0} .answer{padding:14px;border:2px solid var(--green);background:#F1F8F2;border-radius:10px;font-weight:800}
table{width:100%;border-collapse:collapse;margin:12px 0} th,td{border:1px solid var(--border);padding:10px;text-align:left} th{background:#edf4fb;color:var(--navy)} svg{max-width:100%;height:auto} .footer{text-align:center;padding:24px;color:#66788a;font-size:.86rem} .navback{display:inline-block;margin-bottom:14px;color:#fff;font-weight:800}
.resource-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:16px;padding-bottom:40px} .resource{background:#fff;border:1px solid var(--border);border-radius:16px;padding:20px}
@media(max-width:850px){.grid{grid-template-columns:repeat(2,1fr)}} @media(max-width:620px){.grid,.resource-grid{grid-template-columns:1fr} .brand{align-items:flex-start;flex-direction:column} .exercise-body{padding:16px} .section{padding:16px} .actions{grid-template-columns:1fr}}
@media print{body{background:#fff} .topbar,.footer,.actions,.navback{display:none!important} .exercise{box-shadow:none;border:none;width:100%;margin:0} .section{break-inside:avoid}}


/* Academy Design System v1.0 refinements */
:root{--shadow-sm:0 4px 14px rgba(11,31,58,.07);--shadow-md:0 14px 34px rgba(11,31,58,.11);--radius-lg:22px;--focus:0 0 0 4px rgba(0,166,199,.18)}
html{scroll-behavior:smooth}
body{background:linear-gradient(180deg,#f7fbff 0,#edf4fa 100%);min-height:100vh}
a:focus-visible,button:focus-visible{outline:none;box-shadow:var(--focus)}
.topbar{position:sticky;top:0;z-index:50;backdrop-filter:blur(12px)}
.brand-nav{display:flex;align-items:center;gap:12px;flex-wrap:wrap}
.brand-nav a{font-size:.88rem;opacity:.88;padding:7px 9px;border-radius:8px}
.brand-nav a:hover{background:rgba(255,255,255,.12);opacity:1}
.hero{background:radial-gradient(circle at 90% 20%,rgba(0,166,199,.16),transparent 34%)}
.card{transition:transform .2s ease,box-shadow .2s ease,border-color .2s ease}
.card:hover{transform:translateY(-4px);box-shadow:var(--shadow-md);border-color:#b7d7eb}
.card .eyebrow{font-size:.75rem;text-transform:uppercase;letter-spacing:.1em;color:#617386;font-weight:800}
.actions .btn{min-height:44px}
.btn:hover{filter:brightness(.97);transform:translateY(-1px)}
.exercise-head{position:relative;overflow:hidden}
.exercise-head:after{content:"";position:absolute;right:-80px;top:-80px;width:240px;height:240px;border-radius:50%;background:rgba(0,166,199,.16)}
.exercise-head>*{position:relative;z-index:1}
.exercise-body{max-width:860px;margin:auto}
.section{box-shadow:var(--shadow-sm)}
.section h2:before{content:"";display:inline-block;width:7px;height:7px;border-radius:50%;background:var(--cyan);margin-right:9px;vertical-align:2px}
.exercise-tools{display:flex;gap:10px;flex-wrap:wrap;margin-top:18px}
.toolbtn{appearance:none;border:1px solid rgba(255,255,255,.55);background:rgba(255,255,255,.10);color:white;border-radius:10px;padding:9px 12px;font-weight:800;cursor:pointer}
.toolbtn:hover{background:rgba(255,255,255,.18)}
.chapter-nav{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-top:28px}
.chapter-nav a{border:1px solid var(--border);background:#fff;padding:14px;border-radius:12px;font-weight:800;color:var(--navy);box-shadow:var(--shadow-sm)}
.chapter-nav a:last-child{text-align:right}
.master-download{background:linear-gradient(135deg,var(--navy),#15558a);color:#fff;border-radius:18px;padding:22px;display:flex;align-items:center;justify-content:space-between;gap:20px;margin:0 0 28px;box-shadow:var(--shadow-md)}
.master-download p{margin:.3rem 0 0;opacity:.85}
.master-download .btn{background:white;color:var(--navy);border-color:white;white-space:nowrap}
.status-strip{display:grid;grid-template-columns:repeat(4,1fr);gap:12px;margin:22px 0}
.status-item{background:white;border:1px solid var(--border);border-radius:14px;padding:14px;text-align:center;box-shadow:var(--shadow-sm)}
.status-item strong{display:block;color:var(--navy);font-size:1.15rem}
.notice{border-left:5px solid var(--gold);background:#fffaf0;padding:16px;border-radius:12px;margin:18px 0}
@media(max-width:700px){.topbar{position:static}.status-strip{grid-template-columns:repeat(2,1fr)}.master-download{align-items:flex-start;flex-direction:column}.chapter-nav{grid-template-columns:1fr}.chapter-nav a:last-child{text-align:left}}