:root{--primary: #4F46E5;--primary-hover: #4338CA;--bg-color: #F3F4F6;--surface: #FFFFFF;--text-main: #111827;--text-muted: #6B7280;--danger: #EF4444;--danger-hover: #DC2626;--border: #E5E7EB;--course-bg: #FFFFFF;--chapter-bg: #F9FAFB;--lesson-bg: #FFFFFF;--ex-bg: #F3F4F6}body{margin:0;font-family:Inter,system-ui,-apple-system,sans-serif;background-color:var(--bg-color);color:var(--text-main)}.layout{min-height:100vh;display:flex;flex-direction:column}.header{background:var(--surface);padding:1rem 2rem;display:flex;justify-content:space-between;align-items:center;border-bottom:1px solid var(--border);box-shadow:0 1px 3px #0000000d;position:sticky;top:0;z-index:10}.header-brand{display:flex;align-items:center;gap:.75rem}.logo{font-size:1.5rem}.header h1{margin:0;font-size:1.25rem;font-weight:600;color:var(--text-main)}.main-content{flex:1;max-width:1000px;width:100%;margin:0 auto;padding:2rem;box-sizing:border-box}.loading{display:flex;flex-direction:column;align-items:center;justify-content:center;height:100vh;gap:1rem;color:var(--text-muted)}.spinner{animation:spin 1s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}.error-banner{background:#fee2e2;color:#991b1b;padding:1rem;border-radius:8px;display:flex;align-items:center;gap:.5rem;margin-bottom:2rem}button{display:flex;align-items:center;gap:.5rem;border:none;border-radius:6px;font-weight:500;cursor:pointer;transition:all .2s;font-family:inherit}.add-btn{background:var(--primary);color:#fff;padding:.5rem 1rem}.add-btn:hover{background:var(--primary-hover)}.logout-btn{background:transparent;color:var(--text-muted);border:1px solid var(--border);padding:.5rem 1rem}.logout-btn:hover{background:var(--border);color:var(--text-main)}.icon-btn{background:transparent;color:var(--text-muted);padding:.5rem;border-radius:4px}.icon-btn:hover{background:var(--border)}.icon-btn.delete:hover{background:#fee2e2;color:var(--danger)}.add-form-inline{display:flex;gap:.75rem;width:100%}.input-wrapper{position:relative;flex:1;display:flex;align-items:center}.input-icon{position:absolute;left:1rem;color:var(--text-muted);display:flex}.input-wrapper input{width:100%;padding:.6rem 1rem .6rem 2.5rem;border:1px solid var(--border);border-radius:6px;font-size:.95rem;box-sizing:border-box;outline:none;transition:border-color .2s}.input-wrapper input:focus,.order-input:focus{border-color:var(--primary);box-shadow:0 0 0 3px #4f46e51a}.order-input{width:80px;padding:.6rem;border:1px solid var(--border);border-radius:6px;outline:none}.item-header{display:flex;justify-content:space-between;align-items:center}.item-title{display:flex;align-items:center;gap:.75rem}.item-title h2,.item-title h3,.item-title h4{margin:0;font-weight:600}.uuid-badge,.order-badge{font-size:.75rem;padding:.2rem .5rem;border-radius:4px;background:var(--border);color:var(--text-muted);font-weight:400}.item-children{margin-top:1rem;padding-left:1.5rem;border-left:2px solid var(--border);display:flex;flex-direction:column;gap:1rem}.course-add{margin-bottom:2rem;background:var(--surface);padding:1.5rem;border-radius:12px;box-shadow:0 1px 3px #0000001a}.course-card{background:var(--course-bg);border-radius:12px;padding:1.5rem;margin-bottom:1.5rem;box-shadow:0 4px 6px -1px #0000000d,0 2px 4px -1px #00000008;border:1px solid var(--border)}.course-header{cursor:pointer}.course-header:hover .item-title{color:var(--primary)}.icon-course{color:#f59e0b}.course-header h2{font-size:1.25rem}.chapter-card{background:var(--chapter-bg);border-radius:8px;padding:1rem;border:1px solid var(--border)}.icon-chapter{color:#3b82f6}.chapter-header h3{font-size:1.1rem}.lesson-card{background:var(--lesson-bg);border-radius:8px;padding:1rem;border:1px solid var(--border)}.icon-lesson{color:#10b981}.lesson-header h4{font-size:1rem}.exercise-card{background:var(--ex-bg);border-radius:6px;padding:.75rem 1rem;border:1px solid var(--border)}.icon-exercise{color:#8b5cf6}.exercise-header span{font-size:.9rem;font-weight:500}.login-container{min-height:100vh;display:flex;align-items:center;justify-content:center;background-color:var(--bg-color, #F3F4F6);font-family:Inter,system-ui,-apple-system,sans-serif}.login-card{background:#fff;padding:3rem 2.5rem;border-radius:16px;box-shadow:0 10px 25px -5px #0000001a,0 8px 10px -6px #0000001a;width:100%;max-width:400px;text-align:center}.login-icon{background:#eef2ff;color:#4f46e5;width:80px;height:80px;border-radius:50%;display:flex;align-items:center;justify-content:center;margin:0 auto 1.5rem}.login-card h1{margin:0 0 .5rem;font-size:1.5rem;color:#111827}.login-card p{color:#6b7280;margin:0 0 2rem;font-size:.95rem;line-height:1.5}.login-form{display:flex;flex-direction:column;gap:1rem}.input-group{position:relative;display:flex;align-items:center}.input-group input{width:100%;padding:.875rem 3rem .875rem 1rem;border:1px solid #D1D5DB;border-radius:8px;font-size:1rem;outline:none;transition:all .2s;box-sizing:border-box}.input-group input:focus{border-color:#4f46e5;box-shadow:0 0 0 3px #4f46e51a}.toggle-visibility{position:absolute;right:1rem;background:none;border:none;color:#9ca3af;cursor:pointer;padding:0;display:flex}.toggle-visibility:hover{color:#4b5563}.login-button{background:#4f46e5;color:#fff;padding:.875rem;border:none;border-radius:8px;font-size:1rem;font-weight:600;cursor:pointer;transition:background-color .2s;width:100%;display:flex;justify-content:center;align-items:center}.login-button:hover{background:#4338ca}