:root{
  --c-primary:#0b5ed7; --c-ink:#111827; --c-muted:#6b7280;
  --c-line:#e5e7eb; --c-bg:#f9fafb; --c-card:#fff;
  --radius:10px; --shadow:0 2px 8px rgba(0,0,0,.06);
}
*{box-sizing:border-box}
html,body{margin:0;padding:0;font-family:system-ui,Segoe UI,Roboto,sans-serif;color:var(--c-ink);background:var(--c-bg);line-height:1.55}
a{color:var(--c-primary);text-decoration:none}
.container{max-width:1140px;margin:0 auto;padding:0 20px}
.site-header{background:#fff;border-bottom:1px solid var(--c-line);position:sticky;top:0;z-index:20}
.header-inner{display:flex;align-items:center;gap:24px;padding:12px 20px}
.brand{font-weight:700;font-size:1.15rem}
.main-nav{display:flex;gap:16px;flex:1}
.main-nav a{color:var(--c-ink)}
.header-auth-slot{margin-left:auto}
.site-main{min-height:60vh;padding:24px 0 48px}
.site-footer{border-top:1px solid var(--c-line);padding:20px 0;color:var(--c-muted);font-size:.9rem;background:#fff}
h1,h2,h3{line-height:1.25}
.btn{display:inline-block;padding:10px 16px;border-radius:var(--radius);border:1px solid transparent;cursor:pointer;font-size:.95rem;background:#fff;color:var(--c-ink)}
.btn-primary{background:var(--c-primary);color:#fff}
.btn-primary:hover{filter:brightness(1.05)}
.btn-ghost{border-color:var(--c-line)}
.hero{padding:64px 20px;text-align:center;background:linear-gradient(180deg,#eef2ff,#fff)}
.hero h1{max-width:780px;margin:0 auto 12px;font-size:2.1rem}
.hero p{max-width:640px;margin:0 auto 20px;color:var(--c-muted)}
.course-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:20px;margin:20px 0}
.course-card{display:block;background:var(--c-card);border:1px solid var(--c-line);border-radius:var(--radius);padding:16px;box-shadow:var(--shadow);color:inherit}
.course-card img{width:100%;height:160px;object-fit:cover;border-radius:8px;margin-bottom:12px}
.course-card h3{margin:0 0 6px;font-size:1.05rem}
.course-card p{margin:0 0 10px;color:var(--c-muted);font-size:.9rem}
.course-card .meta, .meta{list-style:none;margin:0;padding:0;font-size:.85rem;color:var(--c-muted)}
.meta li{margin:2px 0}
.meta-lg li{margin:4px 0;font-size:.95rem}
.course-header{padding:20px 0 12px;border-bottom:1px solid var(--c-line);margin-bottom:24px}
.preview-section, .course-body, .enroll-section{margin:28px 0}
.preview-item{margin:16px 0;padding:14px;background:#fff;border:1px solid var(--c-line);border-radius:var(--radius)}
.preview-item video{width:100%;max-height:420px;border-radius:8px;background:#000}
.note{color:var(--c-muted);font-size:.85rem}
.prose{max-width:760px}
.prose h2{margin-top:32px}
/* Modals */
.modal{position:fixed;inset:0;z-index:50;display:flex;align-items:center;justify-content:center}
.modal.hidden{display:none}
.modal-backdrop{position:absolute;inset:0;background:rgba(0,0,0,.55)}
.modal-panel{position:relative;background:#fff;border-radius:12px;padding:24px;max-width:420px;width:calc(100% - 40px);box-shadow:0 10px 40px rgba(0,0,0,.2);z-index:1}
.modal-close{position:absolute;top:8px;right:12px;border:0;background:transparent;font-size:22px;cursor:pointer}
.tabs{display:flex;gap:8px;margin-bottom:16px}
.tab{padding:8px 14px;background:transparent;border:1px solid var(--c-line);border-radius:8px;cursor:pointer}
.tab.active{background:var(--c-primary);color:#fff;border-color:var(--c-primary)}
.tab-panel{display:none;flex-direction:column;gap:10px}
.tab-panel.active{display:flex}
.tab-panel label{display:flex;flex-direction:column;gap:4px;font-size:.9rem}
.tab-panel input{padding:9px 10px;border:1px solid var(--c-line);border-radius:8px;font-size:.95rem}
.form-error{color:#b91c1c;font-size:.85rem;margin:0}
/* User menu */
.user-menu{position:relative}
.dropdown{position:absolute;right:0;top:calc(100% + 6px);background:#fff;border:1px solid var(--c-line);border-radius:8px;box-shadow:var(--shadow);min-width:180px;display:flex;flex-direction:column;padding:6px}
.dropdown.hidden{display:none}
.dropdown a, .dropdown button{text-align:left;padding:8px 10px;border:0;background:transparent;cursor:pointer;font-size:.9rem;border-radius:6px;color:var(--c-ink)}
.dropdown a:hover, .dropdown button:hover{background:var(--c-bg)}