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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #e8f1f8 0%, #f5f8fb 100%);
    min-height: 100vh;
}

/* Header */
.header {
    background: linear-gradient(135deg, #1e3a5f 0%, #2d5a8c 100%);
    padding: 20px 40px;
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

.nav-container {
    max-width: 1600px;
    margin: 0 auto;
    display: flex;
    align-items: center;
    justify-content: space-between;
}

.logo-section {
    display: flex;
    align-items: center;
    gap: 15px;
}

.logo-icon {
    width: 50px;
    height: 50px;
    background: white;
    border-radius: 10px;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    color: #1e3a5f;
    font-weight: bold;
}

.logo-text {
    font-size: 24px;
    font-weight: 700;
    color: white;
}

.logo-text .highlight {
    color: #00d4ff;
}

.header-actions {
    display: flex;
    gap: 20px;
    align-items: center;
}

.user-name {
    color: white;
    font-size: 14px;
}

.btn-join {
    background: #00d4ff;
    color: #1e3a5f;
    border: none;
    padding: 10px 28px;
    border-radius: 25px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s;
    font-size: 14px;
    text-decoration: none;
    display: inline-block;
}

.btn-join:hover {
    background: #00b8e6;
    transform: translateY(-2px);
}

/* Main Container */
.container {
    display: flex;
    max-width: 1600px;
    margin: 0 auto;
    padding: 30px;
    gap: 30px;
}

/* Sidebar */
.sidebar {
    width: 280px;
    background: linear-gradient(135deg, #2d5a8c 0%, #1e3a5f 100%);
    border-radius: 20px;
    padding: 0;
    box-shadow: 0 8px 24px rgba(0,0,0,0.15);
    height: fit-content;
}

.sidebar-section {
    padding: 25px;
}

.sidebar-header {
    color: white;
    font-size: 14px;
    display: flex;
    align-items: center;
    gap: 8px;
    margin-bottom: 20px;
    opacity: 0.9;
}

.sidebar-item {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 12px 15px;
    margin-bottom: 8px;
    border-radius: 10px;
    color: white;
    cursor: pointer;
    transition: all 0.3s;
    text-decoration: none;
}

.sidebar-item:hover {
    background: rgba(255,255,255,0.1);
}

.sidebar-item.active {
    background: rgba(0,212,255,0.2);
    border-left: 3px solid #00d4ff;
}

.sidebar-item-content {
    display: flex;
    align-items: center;
    gap: 12px;
}

.sidebar-item-icon {
    font-size: 18px;
}

.sidebar-item-text {
    font-size: 14px;
    font-weight: 500;
}

.sidebar-item-badge {
    font-size: 11px;
    padding: 3px 10px;
    border-radius: 12px;
    background: rgba(255,255,255,0.2);
}

/* Dashboard Section */
.dashboard-section {
    background: white;
    border-radius: 15px;
    padding: 25px;
    margin-top: 20px;
}

.dashboard-title {
    color: #1e3a5f;
    font-size: 16px;
    font-weight: 700;
    margin-bottom: 20px;
}

.progress-circle {
    width: 140px;
    height: 140px;
    margin: 20px auto;
    position: relative;
}

.progress-circle svg {
    transform: rotate(-90deg);
}

.progress-circle-bg {
    fill: none;
    stroke: #e0e0e0;
    stroke-width: 10;
}

.progress-circle-fill {
    fill: none;
    stroke: #00d4ff;
    stroke-width: 10;
    stroke-dasharray: 377;
    stroke-dashoffset: 75.4;
    stroke-linecap: round;
    transition: stroke-dashoffset 0.5s ease;
}

.progress-text {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    font-size: 32px;
    font-weight: 700;
    color: #1e3a5f;
}

.badges {
    display: flex;
    justify-content: center;
    gap: 10px;
    margin-top: 20px;
}

.badge {
    width: 45px;
    height: 45px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 20px;
    font-weight: 700;
    cursor: pointer;
    transition: transform 0.3s;
}

.badge:hover {
    transform: scale(1.1);
}

.badge.blue { background: #4a90e2; color: white; }
.badge.yellow { background: #f5b942; color: white; }
.badge.orange { background: #ff9f43; color: white; }
.badge.gray { background: #95a5a6; color: white; }
.badge.silver { background: #bdc3c7; color: white; }

.badge-label {
    text-align: center;
    font-size: 10px;
    color: #666;
    margin-top: 5px;
}

/* Main Content */
.main-content {
    flex: 1;
}

.hero-section {
    background: white;
    border-radius: 20px;
    padding: 60px 50px;
    margin-bottom: 40px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
}

.hero-title {
    font-size: 52px;
    font-weight: 800;
    color: #1e3a5f;
    margin-bottom: 15px;
    line-height: 1.2;
}

.hero-subtitle {
    font-size: 22px;
    color: #00d4ff;
    margin-bottom: 30px;
    font-weight: 500;
}

.btn-start {
    background: #00d4ff;
    color: white;
    border: none;
    padding: 16px 40px;
    border-radius: 30px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s;
    box-shadow: 0 4px 15px rgba(0,212,255,0.3);
    text-decoration: none;
    display: inline-block;
}

.btn-start:hover {
    background: #00b8e6;
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0,212,255,0.4);
}

/* Course Grid */
.course-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 25px;
}

.course-card {
    background: linear-gradient(135deg, #2d5a8c 0%, #4a7ec9 100%);
    border-radius: 20px;
    padding: 30px;
    color: white;
    position: relative;
    overflow: hidden;
    cursor: pointer;
    transition: all 0.3s;
    box-shadow: 0 4px 15px rgba(0,0,0,0.1);
}

.course-card::before {
    content: '';
    position: absolute;
    top: -50%;
    right: -50%;
    width: 200%;
    height: 200%;
    background: radial-gradient(circle, rgba(255,255,255,0.1) 0%, transparent 70%);
    opacity: 0;
    transition: opacity 0.3s;
}

.course-card:hover {
    transform: translateY(-5px);
    box-shadow: 0 8px 25px rgba(0,0,0,0.2);
}

.course-card:hover::before {
    opacity: 1;
}

.course-icon {
    width: 45px;
    height: 45px;
    background: rgba(255,255,255,0.2);
    border-radius: 12px;
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 20px;
    font-size: 20px;
}

.course-title {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 15px;
    min-height: 44px;
}

.progress-bar {
    width: 100%;
    height: 6px;
    background: rgba(255,255,255,0.2);
    border-radius: 3px;
    overflow: hidden;
    margin-top: 20px;
}

.progress-fill {
    height: 100%;
    background: #00d4ff;
    border-radius: 3px;
    transition: width 0.5s;
}

.course-status {
    position: absolute;
    top: 20px;
    right: 20px;
    background: #00d4ff;
    width: 30px;
    height: 30px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 16px;
}

.course-badge {
    position: absolute;
    top: 20px;
    right: 20px;
    background: rgba(0,212,255,0.2);
    padding: 5px 15px;
    border-radius: 15px;
    font-size: 11px;
    font-weight: 600;
}

/* Login Page */
.login-page {
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    background: linear-gradient(135deg, #1e3a5f 0%, #4a7ec9 100%);
}

.login-container {
    width: 100%;
    max-width: 450px;
    padding: 20px;
}

.login-card {
    background: white;
    border-radius: 20px;
    padding: 50px 40px;
    box-shadow: 0 8px 30px rgba(0,0,0,0.2);
}

.login-card .logo-section {
    justify-content: center;
    margin-bottom: 30px;
}

.login-card h1 {
    font-size: 28px;
    color: #1e3a5f;
    text-align: center;
}

.login-card h2 {
    font-size: 24px;
    color: #1e3a5f;
    margin-bottom: 10px;
    text-align: center;
}

.subtitle {
    text-align: center;
    color: #666;
    margin-bottom: 30px;
}

.login-form {
    margin-top: 30px;
}

.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
    color: #1e3a5f;
    font-weight: 600;
    font-size: 14px;
}

.form-group input {
    width: 100%;
    padding: 12px 15px;
    border: 2px solid #e0e0e0;
    border-radius: 10px;
    font-size: 14px;
    transition: all 0.3s;
}

.form-group input:focus {
    outline: none;
    border-color: #00d4ff;
}

.btn-primary {
    width: 100%;
    background: #00d4ff;
    color: white;
    border: none;
    padding: 14px;
    border-radius: 10px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s;
    margin-top: 10px;
}

.btn-primary:hover {
    background: #00b8e6;
    transform: translateY(-2px);
}

.signup-link {
    text-align: center;
    margin-top: 20px;
    color: #666;
    font-size: 14px;
}

.signup-link a {
    color: #00d4ff;
    text-decoration: none;
    font-weight: 600;
}

.signup-link a:hover {
    text-decoration: underline;
}

.alert {
    padding: 12px 15px;
    border-radius: 8px;
    margin-bottom: 20px;
    font-size: 14px;
}

.alert-error {
    background: #fee;
    color: #c33;
    border: 1px solid #fcc;
}

.alert-success {
    background: #efe;
    color: #3c3;
    border: 1px solid #cfc;
}

/* Lesson Page */
.lesson-container {
    max-width: 1000px;
    margin: 0 auto;
    padding: 30px;
}

.lesson-header {
    background: white;
    border-radius: 20px;
    padding: 40px;
    margin-bottom: 30px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
}

.lesson-header h1 {
    color: #1e3a5f;
    font-size: 36px;
    margin-bottom: 10px;
}

.lesson-header p {
    color: #666;
    font-size: 18px;
    margin-bottom: 20px;
}

.lesson-progress-bar {
    width: 100%;
    height: 8px;
    background: #e0e0e0;
    border-radius: 4px;
    overflow: hidden;
    margin-top: 20px;
}

.lesson-progress-fill {
    height: 100%;
    background: #00d4ff;
    border-radius: 4px;
    transition: width 0.5s;
}

.progress-text {
    margin-top: 10px;
    color: #666;
    font-size: 14px;
}

.lesson-content {
    background: white;
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
}

.lesson-section {
    margin-bottom: 40px;
}

.content-section {
    background: #f9f9f9;
    border-left: 4px solid #00d4ff;
    padding: 25px;
    border-radius: 8px;
}

.content-section h2 {
    color: #1e3a5f;
    font-size: 24px;
    margin-bottom: 15px;
}

.content-section p {
    color: #333;
    line-height: 1.7;
    font-size: 16px;
}

.code-example {
    background: #f5f5f5;
    border-radius: 10px;
    overflow: hidden;
    margin: 20px 0;
}

.code-header {
    background: #1e3a5f;
    color: white;
    padding: 12px 20px;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.try-button {
    background: #00d4ff;
    color: white;
    border: none;
    padding: 6px 16px;
    border-radius: 20px;
    font-size: 13px;
    cursor: pointer;
    transition: background 0.3s;
}

.try-button:hover {
    background: #00b8e6;
}

.code-example pre {
    margin: 0;
    padding: 20px;
    background: white;
    overflow-x: auto;
}

.code-example code {
    font-family: 'Courier New', monospace;
    font-size: 14px;
    line-height: 1.6;
}

.btn-next-section {
    background: #00d4ff;
    color: white;
    border: none;
    padding: 12px 30px;
    border-radius: 25px;
    font-size: 14px;
    font-weight: 600;
    cursor: pointer;
    margin-top: 20px;
    transition: all 0.3s;
}

.btn-next-section:hover {
    background: #00b8e6;
    transform: translateY(-2px);
}

.lesson-complete-section {
    text-align: center;
    padding: 30px 0;
}

.btn-complete {
    background: #00d4ff;
    color: white;
    border: none;
    padding: 16px 40px;
    border-radius: 30px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s;
    margin-right: 15px;
}

.btn-complete:hover {
    background: #00b8e6;
    transform: translateY(-2px);
}

.btn-secondary {
    background: #f0f0f0;
    color: #1e3a5f;
    border: none;
    padding: 16px 40px;
    border-radius: 30px;
    font-size: 16px;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s;
    text-decoration: none;
    display: inline-block;
}

.btn-secondary:hover {
    background: #e0e0e0;
}

/* Quiz Page */
.quiz-container {
    max-width: 900px;
    margin: 0 auto;
    padding: 30px;
}

.quiz-header {
    background: white;
    border-radius: 20px;
    padding: 40px;
    margin-bottom: 30px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
}

.quiz-header h1 {
    color: #1e3a5f;
    font-size: 36px;
    margin-bottom: 10px;
}

.quiz-header p {
    color: #666;
    font-size: 18px;
    margin-bottom: 20px;
}

.quiz-info {
    display: flex;
    gap: 30px;
    font-size: 16px;
    color: #666;
}

.quiz-content {
    background: white;
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
    margin-bottom: 20px;
}

.question-card h3 {
    color: #1e3a5f;
    font-size: 18px;
    margin-bottom: 15px;
}

.question-text {
    font-size: 20px;
    color: #333;
    margin-bottom: 25px;
    font-weight: 500;
}

.options {
    display: flex;
    flex-direction: column;
    gap: 15px;
}

.option {
    display: flex;
    align-items: center;
    padding: 15px 20px;
    border: 2px solid #e0e0e0;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.3s;
}

.option:hover {
    border-color: #00d4ff;
    background: #f0f9ff;
}

.option.selected {
    border-color: #00d4ff;
    background: #e6f7ff;
}

.option input[type="radio"] {
    margin-right: 15px;
    width: 20px;
    height: 20px;
    cursor: pointer;
}

.option span {
    font-size: 16px;
    color: #333;
}

.quiz-navigation {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 20px;
    background: white;
    border-radius: 20px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
}

.question-counter {
    color: #666;
    font-weight: 600;
}

.quiz-results {
    background: white;
    border-radius: 20px;
    padding: 50px;
    box-shadow: 0 4px 20px rgba(0,0,0,0.08);
    text-align: center;
}

.quiz-results h2 {
    color: #1e3a5f;
    font-size: 36px;
    margin-bottom: 30px;
}

.result-score {
    margin: 40px 0;
}

.score-circle {
    width: 200px;
    height: 200px;
    margin: 0 auto;
    position: relative;
}

.result-details {
    background: #f9f9f9;
    border-radius: 15px;
    padding: 30px;
    margin: 30px 0;
}

.result-details p {
    font-size: 18px;
    color: #333;
    margin-bottom: 15px;
}

.result-details strong {
    color: #00d4ff;
}

.result-actions {
    display: flex;
    gap: 15px;
    justify-content: center;
    margin-top: 30px;
}

/* Responsive */
@media (max-width: 1200px) {
    .container {
        flex-direction: column;
    }

    .sidebar {
        width: 100%;
    }

    .course-grid {
        grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
    }
}

@media (max-width: 768px) {
    .header {
        padding: 15px 20px;
    }

    .logo-text {
        font-size: 16px;
    }

    .hero-title {
        font-size: 36px;
    }

    .hero-subtitle {
        font-size: 18px;
    }

    .hero-section {
        padding: 40px 30px;
    }

    .course-grid {
        grid-template-columns: 1fr;
    }

    .lesson-header h1 {
        font-size: 28px;
    }

    .quiz-header h1 {
        font-size: 28px;
    }
}