:root{color-scheme:light;--color-bg:#f7f7fb;--color-surface:#fff;--color-text:#1c1c28;--color-muted:#6b7280;--color-primary:#2563eb;--color-primary-dark:#1d4ed8;--color-border:#e5e7eb;font-family:Inter,-apple-system,BlinkMacSystemFont,Segoe UI,sans-serif}body{margin:0;background:var(--color-bg);color:var(--color-text)}a{color:inherit;text-decoration:none}*{box-sizing:border-box}main{min-height:100vh;display:flex;flex-direction:column}.container{width:min(960px,calc(100% - 2rem));margin:0 auto;padding:2rem 0}.card{background:var(--color-surface);border-radius:1rem;border:1px solid var(--color-border);padding:2rem;box-shadow:0 20px 45px rgba(15,23,42,.1)}button{background:var(--color-primary);color:#fff;border:none;border-radius:.75rem;padding:.75rem 1.5rem;font-weight:600;cursor:pointer;transition:background .2s ease}button:hover{background:var(--color-primary-dark)}button:disabled{opacity:.7;cursor:not-allowed}input,select,textarea{width:100%;padding:.75rem 1rem;border-radius:.75rem;border:1px solid var(--color-border);font-size:1rem;font-family:inherit}label{display:flex;flex-direction:column;gap:.5rem;font-weight:600}@media (max-width:768px){.container{padding:1.5rem 0}.card{padding:1.5rem}}.layout-wrapper{display:flex;min-height:calc(100vh - 140px)}.layout-main{flex:1 1;min-width:0;display:flex;flex-direction:column}.container-fluid{width:100%;max-width:100%;padding:1.5rem}.sidebar{width:256px;flex-shrink:0;background:var(--color-bg);transition:width .2s ease,transform .2s ease;overflow-y:auto;overflow-x:hidden}.sidebar.collapsed{width:56px}.sidebar-header{display:flex;align-items:center;justify-content:space-between;padding:1rem;border-bottom:1px solid var(--color-border)}.sidebar-content{padding:.5rem}.sidebar-toggle{display:flex;align-items:center;justify-content:center;width:32px;height:32px;padding:0;background:transparent;border:1px solid var(--color-border);border-radius:6px;cursor:pointer;color:var(--color-muted);transition:background .15s ease,color .15s ease}.sidebar-toggle:hover{background:var(--color-bg);color:var(--color-text)}.course-tree{list-style:none;margin:0;padding:0}.course-item{margin-bottom:.25rem}.course-item-header{display:flex;align-items:center;gap:.5rem;padding:.5rem .75rem;border-radius:6px;cursor:pointer;font-size:.875rem;transition:background .15s ease}.course-item-header:hover{background:var(--color-bg)}.course-item-header.active{background:rgba(37,99,235,.1);color:var(--color-primary)}.course-item-chevron,.course-item-icon{width:16px;height:16px;flex-shrink:0;color:var(--color-muted)}.course-item-chevron{transition:transform .15s ease}.course-item-chevron.expanded{transform:rotate(90deg)}.course-children{padding-left:1.25rem}.viewer-container{width:100%;max-width:1600px;margin:0 auto;padding:1rem 1.5rem;background:var(--color-surface)}@media (max-width:767px){.sidebar{position:fixed;left:0;top:0;height:100vh;z-index:50;transform:translateX(-100%)}.sidebar.open{transform:translateX(0)}.sidebar-backdrop{position:fixed;inset:0;background:rgba(0,0,0,.5);z-index:40;opacity:0;pointer-events:none;transition:opacity .2s ease}.sidebar-backdrop.visible{opacity:1;pointer-events:auto}.viewer-container{padding:1rem}.mobile-menu-btn{display:flex}}@media (min-width:768px){.mobile-menu-btn,.sidebar-backdrop{display:none}}.header-full-width{background:var(--color-surface);border-bottom:1px solid var(--color-border);padding:0 1.5rem}.header-content{justify-content:space-between;height:60px;max-width:100%}.header-content,.header-logo{display:flex;align-items:center}.header-logo{gap:.5rem;font-size:1.125rem;font-weight:700;text-decoration:none;color:inherit}.header-logo img{height:28px;width:28px}.header-nav{display:flex;align-items:center;gap:.25rem}.header-nav-link{padding:.5rem 1rem;font-size:.9rem;font-weight:500;color:var(--color-muted);border-radius:.5rem;transition:color .15s,background .15s}.header-nav-link:hover{color:var(--color-text);background:var(--color-bg)}.hero-section{background:linear-gradient(135deg,#1e3a5f,#2563eb);color:#fff;padding:4rem 1.5rem}.hero-inner{width:min(720px,100%);margin:0 auto;text-align:center}.hero-title{margin:0;font-size:2.25rem;font-weight:800;line-height:1.2}.hero-subtitle{margin:1rem 0 2rem;font-size:1.1rem;opacity:.85;line-height:1.5}.hero-inner>div{justify-content:center}.btn-primary{display:inline-flex;align-items:center;padding:.75rem 1.75rem;font-size:1rem;font-weight:600;background:#fff;color:#1e3a5f;border-radius:.5rem;text-decoration:none;transition:background .15s,transform .1s}.btn-primary:hover{background:#f0f4ff;transform:translateY(-1px)}.btn-secondary{display:inline-flex;align-items:center;padding:.75rem 1.75rem;font-size:1rem;font-weight:600;background:hsla(0,0%,100%,.15);color:#fff;border:1px solid hsla(0,0%,100%,.3);border-radius:.5rem;text-decoration:none;transition:background .15s,transform .1s}.btn-secondary:hover{background:hsla(0,0%,100%,.25);transform:translateY(-1px)}.course-card{transition:border-color .15s,box-shadow .15s;cursor:pointer;text-decoration:none;color:inherit}.course-card:hover{border-color:var(--color-primary);box-shadow:0 4px 20px rgba(37,99,235,.1)}.features-grid{display:grid;grid-template-columns:repeat(3,1fr);grid-gap:1.5rem;gap:1.5rem;margin-top:3rem}.feature-item{text-align:center;padding:1.5rem 1rem}.feature-icon{font-size:1.75rem;margin-bottom:.75rem}.feature-title{margin:0 0 .5rem;font-size:1rem}.feature-desc{margin:0;font-size:.875rem;color:var(--color-muted);line-height:1.5}@media (max-width:768px){.hero-section{padding:2.5rem 1.5rem}.hero-title{font-size:1.75rem}.features-grid{grid-template-columns:1fr;gap:1rem}}.footer-full-width{margin-top:auto;background:var(--color-surface);border-top:1px solid var(--color-border);padding:1.5rem}.footer-content{display:flex;flex-direction:column;gap:.5rem}