@import url('https://fonts.googleapis.com/css2?family=Noto+Sans+KR:wght@400;500;700&display=swap');

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

body {
    font-family: 'Noto Sans KR', sans-serif;
    background: linear-gradient(135deg, #f5f7fa, #c3cfe2);
    color: #333;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
    line-height: 1.6;
}

.container {
    background-color: white;
    padding: 40px;
    border-radius: 20px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.08);
    width: 100%;
    max-width: 700px;
    text-align: center;
    position: relative;
    animation: fadeIn 0.8s ease-out;
    border-top: 5px solid #007bff;
    margin: 20px;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

.header-section {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 15px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}

h1 {
    color: #1a2a40;
    margin: 0;
    font-size: clamp(1.8em, 5vw, 2.5em);
    font-weight: 700;
}

.youtube-link {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 40px;
    height: 40px;
    background: #ff0000;
    border-radius: 8px;
    text-decoration: none;
    transition: all 0.3s ease;
    box-shadow: 0 2px 8px rgba(255, 0, 0, 0.2);
}

.youtube-link:hover {
    transform: translateY(-1px);
    box-shadow: 0 4px 12px rgba(255, 0, 0, 0.3);
    background: #e60000;
}

.youtube-logo {
    width: 24px;
    height: 24px;
    fill: white;
}

.subtitle {
    font-size: clamp(1em, 2vw, 1.1em);
    color: #666;
    margin-bottom: 40px;
    line-height: 1.6;
}

.subject-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
    margin-top: 30px;
}

.subject-cards-container {
    display: flex;
    gap: 20px;
    margin: 30px 0;
}

.subject-card {
    background: linear-gradient(45deg, #007bff, #0056b3);
    color: white;
    border: none;
    padding: 30px 20px;
    border-radius: 12px;
    cursor: pointer;
    font-size: clamp(0.9em, 2.5vw, 1em);
    font-weight: 500;
    text-decoration: none;
    display: block;
    transition: all 0.3s cubic-bezier(0.25, 0.8, 0.25, 1);
    box-shadow: 0 4px 15px rgba(0, 123, 255, 0.2);
    position: relative;
    overflow: hidden;
    flex: 1;
}

.subject-card:hover {
    background: linear-gradient(45deg, #0056b3, #004494);
    transform: translateY(-3px);
    box-shadow: 0 6px 20px rgba(0, 123, 255, 0.3);
}

.subject-card.geography {
    background: linear-gradient(45deg, #007bff, #0056b3);
}

.subject-card.english {
    background: linear-gradient(45deg, #28a745, #1e7e34);
}

.subject-card.english:hover {
    background: linear-gradient(45deg, #1e7e34, #1a6c2e);
    box-shadow: 0 6px 20px rgba(40, 167, 69, 0.3);
}

.subject-card.math {
    background: linear-gradient(45deg, #dc3545, #c82333);
}

.subject-card.math:hover {
    background: linear-gradient(45deg, #c82333, #bd2130);
    box-shadow: 0 6px 20px rgba(220, 53, 69, 0.3);
}

.subject-card.science {
    background: linear-gradient(45deg, #6f42c1, #563d7c);
}

.subject-card.science:hover {
    background: linear-gradient(45deg, #563d7c, #4c366d);
    box-shadow: 0 6px 20px rgba(111, 66, 193, 0.3);
}

.subject-card.coming-soon {
    background: #cccccc;
    cursor: not-allowed;
    transform: none;
    box-shadow: none;
    opacity: 0.7;
}

.subject-card.coming-soon:hover {
    background: #cccccc;
    transform: none;
    box-shadow: none;
}

.subject-icon {
    font-size: 3em;
    margin-bottom: 15px;
    display: block;
}

.subject-title {
    font-size: 1.4em;
    font-weight: 700;
    margin-bottom: 10px;
}

.subject-description {
    font-size: 0.9em;
    opacity: 0.9;
    line-height: 1.4;
}

.footer {
    margin-top: 40px;
    padding-top: 30px;
    border-top: 1px solid #ecf0f1;
    color: #666;
    font-size: clamp(0.8em, 2vw, 0.9em);
}

.footer a {
    color: #007bff;
    text-decoration: none;
}

.footer a:hover {
    text-decoration: underline;
}

@media (max-width: 600px) {
    body {
        padding: 10px;
    }
    
    .container {
        padding: 25px;
        margin: 10px;
    }
    
    .header-section {
        gap: 10px;
    }
    
    .youtube-link {
        width: 35px;
        height: 35px;
    }
    
    .youtube-logo {
        width: 20px;
        height: 20px;
    }
    
    .subject-cards-container {
        flex-direction: column;
        gap: 15px;
    }
}