:root { 
    --primary: #6366f1; 
    --bg: #f8fafc; 
    --sidebar-bg: #0f172a; 
    --text-main: #1e293b; 
    --border: #e2e8f0; 
    --purple: #8b5cf6;
    --emerald: #10b981;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

body { 
    font-family: 'Plus Jakarta Sans', sans-serif; 
    background: var(--bg); 
    height: 100vh; 
    display: flex; 
    overflow: hidden; 
}

/* Sidebar Styling */
.sidebar { width: 320px; background: #fff; color: var(--text-main); display: flex; flex-direction: column; border-right: 1px solid var(--border); z-index: 10; }
.sidebar-header { padding: 30px; border-bottom: 1px solid var(--border); }
.logo { font-size: 1.5rem; font-weight: 800; display: flex; align-items: center; gap: 12px; background: linear-gradient(135deg, var(--primary) 0%, #4f46e5 100%); -webkit-background-clip: text; -webkit-text-fill-color: transparent; }
.session-list { flex: 1; overflow-y: auto; padding: 20px; scrollbar-width: thin; scrollbar-color: var(--border) transparent; }
.session-item { display: flex; flex-direction: column; padding: 14px 18px; border-radius: 14px; cursor: pointer; color: #64748b; text-decoration: none; margin-bottom: 8px; transition: 0.2s; border: 1px solid transparent; }
.session-item:hover { background: #f8fafc; color: var(--primary); border-color: var(--border); }
.session-item.active { background: linear-gradient(135deg, var(--primary) 20%, #4f46e5 100%); color: #fff; box-shadow: 0 8px 15px rgba(99, 102, 241, 0.2); }
.session-item .date { font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.05em; opacity: 0.7; margin-bottom: 4px; }
.session-item .title { font-size: 0.9rem; font-weight: 600; line-height: 1.4; }

/* Main Content Area */
.main-content { flex: 1; display: flex; flex-direction: column; background: #fff; }
header { padding: 20px 40px; background: #fff; border-bottom: 1px solid var(--border); display: flex; justify-content: space-between; align-items: center; }

/* Action Buttons */
.header-actions { display: flex; gap: 12px; align-items: center; }
.btn-action { 
    padding: 10px 20px; border-radius: 12px; border: 1px solid transparent; 
    font-weight: 700; cursor: pointer; display: flex; align-items: center; 
    gap: 8px; transition: all 0.3s; text-decoration: none; font-size: 0.85rem; 
    box-shadow: 0 1px 2px rgba(0,0,0,0.05); white-space: nowrap; 
}
.btn-action:hover { transform: translateY(-2px); box-shadow: 0 4px 12px rgba(0,0,0,0.08); }
.edit-btn { background: #f8fafc; color: #475569; border-color: var(--border); }
.edit-btn.editing { background: #fff1f2; color: #e11d48; border-color: #fecdd3; }
.save-btn { background: var(--emerald); color: white; }
.note-toggle-btn { background: linear-gradient(135deg, #6366f1 0%, #4f46e5 100%); color: white; }

/* Info Bar (Video/Resources) */
.info-bar { padding: 25px 40px; background: #fcfcfd; border-bottom: 1px solid var(--border); display: none; }
.info-bar.active { display: block; animation: slideDown 0.4s ease; }
@keyframes slideDown { from { opacity: 0; transform: translateY(-10px); } to { opacity: 1; transform: translateY(0); } }

.resource-row { display: flex; gap: 12px; flex-wrap: wrap; margin-top: 15px; }
.btn-res { display: flex; align-items: center; gap: 8px; padding: 10px 18px; background: #fff; border-radius: 12px; text-decoration: none; color: #1e293b; font-size: 0.82rem; font-weight: 700; border: 1px solid var(--border); transition: 0.2s; }
.btn-res:hover { border-color: var(--primary); color: var(--primary); background: #f5f3ff; }
.btn-yt { border-color: #fecaca; color: #ef4444; }
.btn-yt:hover { background: #fef2f2; border-color: #f87171; }

/* Content Area (Iframe) */
.iframe-container { flex: 1; background: #f1f5f9; position: relative; }
iframe { width: 100%; height: 100%; border: none; background: white; }

.welcome { position: absolute; top: 0; left: 0; width: 100%; height: 100%; display: flex; flex-direction: column; align-items: center; justify-content: center; text-align: center; background: #fff; z-index: 5; padding: 40px; }
.welcome h2 { font-size: 1.8rem; color: #0f172a; margin-bottom: 10px; }
.welcome p { color: #64748b; max-width: 400px; }