*{box-sizing:border-box}
body{margin:0;background:#f8fafc;color:#1e293b;font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;line-height:1.6}

/* Header */
header,.app-header{height:60px;padding:0 24px;display:flex;align-items:center;justify-content:space-between;background:#ffffff;border-bottom:1px solid #e2e8f0;position:sticky;top:0;z-index:100}
.header-left{display:flex;align-items:center;gap:12px}
.back-link{color:#2563eb;text-decoration:none;font-weight:600;font-size:0.95rem}
.back-link:hover{text-decoration:underline}
.header-divider{color:#cbd5e1}
.header-title{font-weight:600;color:#334155;font-size:0.95rem;max-width:500px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}

header form,.app-header form{margin:0;display:inline-flex;align-items:center}
.header-right{display:flex;align-items:center;gap:12px}
.nav-link{color:#475569;text-decoration:none;font-weight:600;font-size:0.88rem;padding:6px 12px;border-radius:6px;transition:all 0.2s}
.nav-link:hover{color:#2563eb;background:#eff6ff}

.logout-btn{margin:0;width:auto;border:1px solid #cbd5e1;background:#ffffff;color:#475569;font-weight:600;cursor:pointer;padding:6px 14px;border-radius:6px;font-size:0.85rem;line-height:1.4;transition:all 0.2s;display:inline-flex;align-items:center}
.logout-btn:hover{background:#f8fafc;color:#ef4444;border-color:#fca5a5}

/* Books Grid */
.container{max-width:1040px;margin:50px auto;padding:0 24px}
h1{font-size:2rem;margin-bottom:8px;color:#0f172a}
.card{background:#fff;border:1px solid #e2e8f0;border-radius:16px;box-shadow:0 4px 20px #0f172a0a}
.books{display:grid;grid-template-columns:repeat(auto-fit,minmax(280px,1fr));gap:20px;margin-top:28px}
.book{padding:26px;text-decoration:none;color:inherit;transition:transform .2s,border-color .2s}
.book:hover{transform:translateY(-3px);border-color:#2563eb}
.book h2{margin:0 0 8px 0;font-size:1.25rem}
.book p{margin:0 0 16px 0;color:#64748b;font-size:0.95rem}
.book span{color:#2563eb;font-weight:600}

/* Center Form Layout */
.center{min-height:100vh;display:grid;place-items:center;padding:20px}
.login{width:min(420px,100%);padding:36px;margin:auto}
.login-header{text-align:center;margin-bottom:24px}
.login-header h1{font-size:1.8rem;margin:0 0 8px 0;color:#0f172a}
.login-header .subtitle{margin:0;color:#64748b;font-size:0.95rem}
.login-footer{text-align:center;margin-top:24px;font-size:0.9rem}
.login-footer a{color:#2563eb;text-decoration:none;font-weight:600}
.login-footer a:hover{text-decoration:underline}

label{display:block;font-weight:600;margin:16px 0 6px;color:#334155;text-align:left}
input{display:block;width:100%;padding:10px 14px;border:1px solid #cbd5e1;border-radius:8px;font-size:1rem;outline:none}
input:focus{border-color:#2563eb;box-shadow:0 0 0 3px #2563eb22}
button{border:0;border-radius:8px;background:#2563eb;color:white;padding:12px 20px;font-weight:700;cursor:pointer;width:100%;margin-top:20px;font-size:1rem}
button:hover{background:#1d4ed8}
.link{background:none;color:#2563eb;width:auto;margin:0;padding:5px}
.error{color:#ef4444;margin-top:16px;font-size:0.9rem;text-align:center}
.success{color:#10b981;margin-top:16px;font-size:0.9rem;text-align:center}

/* Doc Reader Layout */
.doc-layout{background:#ffffff}
.doc-container{display:flex;min-height:calc(100vh - 60px)}

/* Sidebar */
.sidebar{width:320px;background:#f8fafc;border-right:1px solid #e2e8f0;flex-shrink:0;height:calc(100vh - 60px);position:sticky;top:60px;overflow-y:auto;padding:20px 12px}
.sidebar-category{margin-bottom:8px}
.category-header{display:flex;align-items:center;padding:4px 6px;border-radius:6px}
.category-header:hover{background:#f1f5f9}
.toggle-btn{border:none;background:none;cursor:pointer;padding:4px;color:#94a3b8;font-size:0.75rem;display:flex;align-items:center;justify-content:center;margin:0;width:24px;height:24px;border-radius:4px}
.toggle-btn:hover{color:#334155;background:#e2e8f0}
.toggle-btn .arrow{display:inline-block;transition:transform .2s ease;font-size:0.65rem}
.sidebar-category.expanded .toggle-btn .arrow{transform:rotate(90deg)}

.category-title-link{flex:1;font-size:0.88rem;font-weight:700;color:#475569;text-decoration:none;padding:4px 6px;border-radius:4px;line-height:1.3}
.category-title-link:hover{color:#0f172a}
.category-title-link.active-cat{color:#2563eb;font-weight:700}

.category-items{list-style:none;padding-left:24px;margin:4px 0 0 0;display:none}
.sidebar-category.expanded .category-items{display:block}
.category-items li{margin-bottom:2px}
.category-items a{display:block;padding:6px 10px;color:#64748b;text-decoration:none;font-size:0.88rem;border-radius:6px;line-height:1.4}
.category-items a:hover{background:#e2e8f0;color:#0f172a}
.category-items a.active{background:#dbeafe;color:#1d4ed8;font-weight:600}

/* Doc Content */
.doc-content{flex:1;max-width:880px;padding:40px 48px;margin:0 auto}

/* Markdown Styling */
.markdown-body{font-size:1.05rem;line-height:1.75;color:#334155}
.markdown-body h1{font-size:2.25rem;border-bottom:1px solid #e2e8f0;padding-bottom:12px;margin-top:0;margin-bottom:24px;color:#0f172a}
.markdown-body h2{font-size:1.6rem;border-bottom:1px solid #f1f5f9;padding-bottom:8px;margin-top:36px;margin-bottom:16px;color:#0f172a}
.markdown-body h3{font-size:1.3rem;margin-top:28px;margin-bottom:12px;color:#1e293b}
.markdown-body h4{font-size:1.1rem;margin-top:20px;margin-bottom:8px;color:#1e293b}
.markdown-body p{margin-bottom:18px}
.markdown-body a{color:#2563eb;text-decoration:none}
.markdown-body a:hover{text-decoration:underline}
.markdown-body img{max-width:100%;height:auto;border-radius:8px;box-shadow:0 4px 12px #0000000f;margin:20px 0}
.markdown-body code{background:#f1f5f9;color:#0f172a;padding:3px 6px;border-radius:4px;font-size:0.9em;font-family:ui-monospace,SFMono-Regular,Consolas,monospace}
.markdown-body pre{background:#0f172a;color:#f8fafc;padding:18px 24px;border-radius:10px;overflow-x:auto;margin:24px 0}
.markdown-body pre code{background:none;color:inherit;padding:0;border-radius:0}
.markdown-body blockquote{border-left:4px solid #2563eb;background:#eff6ff;margin:20px 0;padding:14px 20px;border-radius:0 8px 8px 0;color:#1e40af}
.markdown-body ul, .markdown-body ol{padding-left:24px;margin-bottom:18px}
.markdown-body li{margin-bottom:6px}
.markdown-body table{width:100%;border-collapse:collapse;margin:24px 0}
.markdown-body th,.markdown-body td{border:1px solid #cbd5e1;padding:10px 14px;text-align:left}
.markdown-body th{background:#f1f5f9;font-weight:600;color:#0f172a}