:root {
    --primary: #667eea;
    --secondary: #764ba2;
    --text: #2d3748;
    --text-light: #718096;
    --bg: #f7fafc;
    --white: #ffffff;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 30px rgba(0, 0, 0, 0.15);
}

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

body {
    font-family: 'Inter', sans-serif;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Navbar */
.navbar {
    background: var(--white);
    box-shadow: var(--shadow);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

.navbar .container {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    display: flex;
    align-items: center;
    gap: 10px;
    text-decoration: none;
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--primary);
}

.logo-icon {
    font-size: 2rem;
}

.nav-links {
    display: flex;
    align-items: center;
    gap: 2rem;
}

.nav-link {
    text-decoration: none;
    color: var(--text);
    font-weight: 500;
    transition: color 0.3s;
}

.nav-link:hover {
    color: var(--primary);
}

.search-form {
    display: flex;
    gap: 5px;
}

.search-input {
    padding: 8px 15px;
    border: 2px solid #e2e8f0;
    border-radius: 20px;
    outline: none;
    transition: border-color 0.3s;
}

.search-input:focus {
    border-color: var(--primary);
}

.search-btn {
    padding: 8px 15px;
    background: var(--primary);
    color: white;
    border: none;
    border-radius: 20px;
    cursor: pointer;
    transition: transform 0.2s;
}

.search-btn:hover {
    transform: scale(1.05);
}

/* Hero */
.hero {
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    color: white;
    padding: 80px 0;
    text-align: center;
}

.hero-title {
    font-size: 3rem;
    margin-bottom: 1rem;
}

.hero-subtitle {
    font-size: 1.5rem;
    opacity: 0.9;
}

/* Topics Grid */
.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
    padding: 60px 0;
}

.topic-card {
    background: var(--white);
    padding: 30px;
    border-radius: 15px;
    text-decoration: none;
    color: var(--text);
    box-shadow: var(--shadow);
    transition: all 0.3s;
    position: relative;
    overflow: hidden;
}

.topic-card::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 5px;
    background: var(--topic-color);
}

.topic-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
}

.topic-icon {
    font-size: 3rem;
    margin-bottom: 15px;
}

.topic-title {
    font-size: 1.5rem;
    margin-bottom: 10px;
}

.topic-count {
    color: var(--text-light);
    margin-bottom: 15px;
}

.topic-arrow {
    font-size: 1.5rem;
    color: var(--topic-color);
}

/* Topic Header */
.topic-header {
    color: white;
    padding: 60px 0;
}

.back-link {
    color: white;
    text-decoration: none;
    display: inline-block;
    margin-bottom: 20px;
    opacity: 0.9;
}

.back-link:hover {
    opacity: 1;
}

.topic-header-title {
    font-size: 2.5rem;
    margin-bottom: 10px;
}

.topic-header-subtitle {
    font-size: 1.2rem;
    opacity: 0.9;
}

/* Subtopics List */
.subtopics-list {
    padding: 60px 0;
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.subtopic-card {
    background: var(--white);
    padding: 25px;
    border-radius: 10px;
    text-decoration: none;
    color: var(--text);
    box-shadow: var(--shadow);
    display: flex;
    align-items: center;
    gap: 20px;
    transition: all 0.3s;
}

.subtopic-card:hover {
    transform: translateX(10px);
    box-shadow: var(--shadow-lg);
}

.subtopic-number {
    width: 50px;
    height: 50px;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    color: white;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 1.2rem;
}

.subtopic-info {
    flex: 1;
}

.subtopic-title {
    font-size: 1.3rem;
    margin-bottom: 5px;
}

.subtopic-description {
    color: var(--text-light);
}

.subtopic-arrow {
    font-size: 1.5rem;
    color: var(--primary);
}

/* Content Page */
.content-header {
    background: var(--white);
    padding: 30px 0;
    border-bottom: 1px solid #e2e8f0;
}

.breadcrumb {
    color: var(--text-light);
    margin-bottom: 15px;
}

.breadcrumb a {
    color: var(--primary);
    text-decoration: none;
}

.content-title {
    font-size: 2.5rem;
}

.content-body {
    padding: 60px 0;
}

.content-placeholder {
    background: var(--white);
    padding: 60px;
    border-radius: 15px;
    text-align: center;
    box-shadow: var(--shadow);
}

.placeholder-icon {
    font-size: 4rem;
    margin-bottom: 20px;
}

.placeholder-instructions {
    margin-top: 40px;
    text-align: left;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

.btn-primary {
    display: inline-block;
    padding: 12px 30px;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    color: white;
    text-decoration: none;
    border-radius: 25px;
    margin-top: 20px;
    transition: transform 0.3s;
}

.btn-primary:hover {
    transform: scale(1.05);
}

/* Footer */
.footer {
    background: var(--text);
    color: white;
    text-align: center;
    padding: 30px 0;
    margin-top: 60px;
}

/* Responsive */
@media (max-width: 768px) {
    .hero-title {
        font-size: 2rem;
    }

    .hero-subtitle {
        font-size: 1.2rem;
    }

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

    .nav-links {
        flex-direction: column;
        gap: 1rem;
    }
}