body { margin: 0; font-family: 'Segoe UI', sans-serif; background: #f0f9ff; color: #334155; }
.hidden { display: none !important; }

/* Login Screen */
.login-container { height: 100vh; display: flex; justify-content: center; align-items: center; background: linear-gradient(135deg, #eff6ff 0%, #dbeafe 100%); }
.login-box { background: white; padding: 40px; border-radius: 24px; width: 90%; max-width: 350px; box-shadow: 0 20px 40px rgba(59, 130, 246, 0.15); text-align: center; }
.input-group { background: #f1f5f9; border-radius: 12px; padding: 12px; margin: 20px 0; display: flex; align-items: center; gap: 10px; border: 1px solid transparent; transition: 0.3s; }
.input-group:focus-within { border-color: #3b82f6; background: white; box-shadow: 0 0 0 4px rgba(59, 130, 246, 0.1); }
input { border: none; background: transparent; width: 100%; outline: none; font-size: 16px; color: #334155; }
/* Style đặc biệt cho ô Code */
#txtCode { font-family: monospace; letter-spacing: 2px; } 

.btn-primary { background: #3b82f6; color: white; border: none; width: 100%; padding: 15px; border-radius: 12px; font-weight: bold; font-size: 16px; cursor: pointer; transition: 0.2s; box-shadow: 0 4px 12px rgba(59, 130, 246, 0.3); }
.btn-primary:active { transform: scale(0.98); }
.btn-primary:disabled { background: #94a3b8; cursor: not-allowed; }
.error-msg { color: #ef4444; font-size: 13px; margin-top: 15px; min-height: 20px; font-weight: 500; }

/* App Header */
.app-header { background: white; padding: 15px 20px; display: flex; justify-content: space-between; align-items: center; position: sticky; top: 0; z-index: 100; box-shadow: 0 2px 10px rgba(0,0,0,0.05); }
.user-info { display: flex; align-items: center; gap: 12px; }
.avatar { width: 45px; height: 45px; background: #dbeafe; color: #3b82f6; border-radius: 50%; display: flex; align-items: center; justify-content: center; font-size: 20px; }
.badge { background: #fef3c7; color: #d97706; padding: 2px 8px; border-radius: 6px; font-size: 11px; font-weight: bold; }
.btn-logout { background: #f1f5f9; border: none; width: 40px; height: 40px; border-radius: 50%; color: #64748b; cursor: pointer; }

/* Content */
.week-selector { padding: 15px 20px; display: flex; align-items: center; gap: 10px; }
.week-selector select { border: none; background: white; padding: 8px 15px; border-radius: 20px; font-weight: bold; color: #3b82f6; box-shadow: 0 2px 5px rgba(0,0,0,0.05); }
.content-area { padding: 0 20px 40px 20px; max-width: 800px; margin: 0 auto; }
.card { background: white; border-radius: 16px; padding: 20px; margin-bottom: 20px; box-shadow: 0 4px 6px rgba(0,0,0,0.02); }
.video-wrapper { position: relative; padding-bottom: 56.25%; height: 0; overflow: hidden; border-radius: 12px; margin-top: 15px; background: #000; }
.video-wrapper iframe { position: absolute; top: 0; left: 0; width: 100%; height: 100%; }
.ex-item { display: flex; gap: 15px; padding: 15px 0; border-bottom: 1px dashed #e2e8f0; }
.ex-item:last-child { border-bottom: none; }
.ex-img { width: 80px; height: 80px; object-fit: cover; border-radius: 8px; background: #f1f5f9; }
.ex-content h4 { margin: 0 0 5px 0; color: #1e293b; }
.ex-desc { font-size: 14px; color: #64748b; line-height: 1.5; }
.empty-state { text-align: center; padding: 50px 0; color: #94a3b8; }