:root {
    --primary-color: #0d0d2b;
    --secondary-color: #1a1a4b;
    --accent-color: #00ffff;
    --text-color: #e0e0e0;
    --font-title: 'Orbitron', sans-serif;
    --font-body: 'Noto Sans KR', sans-serif;
}

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

html {
    scroll-behavior: smooth;
}

body {
    font-family: var(--font-body);
    background-color: var(--primary-color);
    color: var(--text-color);
    line-height: 1.7;
}

header {
    position: fixed;
    width: 100%;
    top: 0;
    left: 0;
    background: rgba(13, 13, 43, 0.8);
    backdrop-filter: blur(10px);
    padding: 1rem 5%;
    z-index: 1000;
    transition: background 0.3s;
}

nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.logo {
    font-family: var(--font-title);
    font-size: 1.5rem;
    color: var(--accent-color);
    text-decoration: none;
    font-weight: 700;
}

nav ul {
    list-style: none;
    display: flex;
    gap: 2rem;
}

nav a {
    color: var(--text-color);
    text-decoration: none;
    font-weight: 700;
    transition: color 0.3s;
}

nav a:hover {
    color: var(--accent-color);
}

.hero {
    height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    text-align: center;
    background-image: linear-gradient(rgba(13, 13, 43, 0.7), rgba(13, 13, 43, 0.9)), url('https://source.unsplash.com/random/1920x1080/?nebula,space');
    background-size: cover;
    background-position: center;
    padding: 0 5%;
}

.hero-content h1 {
    font-family: var(--font-title);
    font-size: 4rem;
    margin-bottom: 1rem;
    color: #fff;
}

.hero-content p {
    font-size: 1.2rem;
    max-width: 600px;
    margin: 0 auto 2rem;
}

.cta-button {
    display: inline-block;
    background: var(--accent-color);
    color: var(--primary-color);
    padding: 0.8rem 2rem;
    border-radius: 5px;
    text-decoration: none;
    font-weight: 700;
    transition: transform 0.3s, box-shadow 0.3s;
}

.cta-button:hover {
    transform: translateY(-3px);
    box-shadow: 0 5px 15px rgba(0, 255, 255, 0.4);
}

.content-section, .topics-section {
    padding: 6rem 5%;
    max-width: 1200px;
    margin: 0 auto;
    opacity: 0;
    transform: translateY(30px);
    transition: opacity 0.6s ease-out, transform 0.6s ease-out;
}

.content-section.visible, .topics-section.visible {
    opacity: 1;
    transform: translateY(0);
}

.content-section h2, .topics-section h2 {
    font-family: var(--font-title);
    font-size: 2.5rem;
    text-align: center;
    margin-bottom: 3rem;
    color: var(--accent-color);
}

.topics-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
}

.topic-card {
    background: var(--secondary-color);
    border-radius: 10px;
    overflow: hidden;
    transition: transform 0.3s, box-shadow 0.3s;
}

.topic-card:hover {
    transform: translateY(-10px);
    box-shadow: 0 10px 20px rgba(0, 0, 0, 0.4);
}

.topic-card img {
    width: 100%;
    height: 200px;
    object-fit: cover;
}

.topic-card h3 {
    font-family: var(--font-title);
    font-size: 1.5rem;
    padding: 1rem 1.5rem 0.5rem;
}

.topic-card p {
    padding: 0 1.5rem 1.5rem;
}

footer {
    background: var(--secondary-color);
    text-align: center;
    padding: 2rem 5%;
    margin-top: 4rem;
}