:root {
    --primary-color: #3b82f6;
    --secondary-color: #10b981;
    --background-color: #f5f7fb;
    --text-color: #1f2937;
    --muted-text-color: #6b7280;
    --white: #fff;
    --danger-color: #ef4444;
    --surface-color: #ffffff;
    --border-color: #e5e7eb;
    --shadow-soft: 0 10px 30px rgba(15, 23, 42, 0.12);
    --shadow-strong: 0 20px 40px rgba(15, 23, 42, 0.18);
    --font-family: "Noto Sans KR", "Apple SD Gothic Neo", "Malgun Gothic", system-ui, -apple-system, sans-serif;
}

body {
    margin: 0;
    font-family: var(--font-family);
    background: radial-gradient(circle at top, #ffffff 0%, #f0f4ff 45%, #eef2ff 100%);
    color: var(--text-color);
}

#app {
    min-height: 100vh;
    position: relative;
}

.initial-view {
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    position: relative;
    z-index: 0;
}

.hero-card {
    background: rgba(255, 255, 255, 0.9);
    border: 1px solid var(--border-color);
    border-radius: 18px;
    padding: 44px 56px;
    box-shadow: var(--shadow-strong);
    text-align: center;
    backdrop-filter: blur(10px);
    position: relative;
    z-index: 1;
    pointer-events: auto;
}

.hero-title {
    margin: 0 0 10px;
    font-size: 30px;
    font-weight: 700;
    letter-spacing: -0.3px;
}

.hero-subtitle {
    margin: 0 0 32px;
    color: var(--muted-text-color);
    font-size: 16px;
}

.hero-features {
    display: flex;
    gap: 14px;
    justify-content: center;
    flex-wrap: wrap;
    margin-bottom: 28px;
}

.hero-feature {
    background: #f8fafc;
    border: 1px solid var(--border-color);
    padding: 8px 14px;
    border-radius: 999px;
    font-size: 13px;
    color: var(--muted-text-color);
}

.button-container {
    display: flex;
    flex-direction: row;
    gap: 30px;
    align-items: center;
}

.button-divider {
    color: var(--muted-text-color);
    font-size: 20px;
    font-weight: 300;
    user-select: none;
}

.btn {
    padding: 24px 48px;
    font-size: 22px;
    min-width: 220px;
    border: none;
    border-radius: 14px;
    cursor: pointer;
    transition: transform 0.2s ease, box-shadow 0.2s ease;
    box-shadow: var(--shadow-soft);
    font-weight: 600;
    letter-spacing: -0.2px;
}

.btn-student {
    background: linear-gradient(135deg, #3b82f6, #6366f1);
    color: var(--white);
}

.btn-teacher {
    background: linear-gradient(135deg, #10b981, #14b8a6);
    color: var(--white);
}

.btn:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-strong);
}

.admin-button {
    position: absolute;
    top: 20px;
    right: 20px;
    padding: 8px 12px;
    font-size: 14px;
    background-color: rgba(255, 255, 255, 0.9);
    border: 1px solid var(--border-color);
    border-radius: 5px;
    cursor: pointer;
    box-shadow: var(--shadow-soft);
    z-index: 2;
}

.app-shell {
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

.app-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 10px;
    padding: 18px 28px;
}

.app-brand {
    font-weight: 700;
    letter-spacing: -0.3px;
    font-size: 18px;
}

.app-content {
    flex: 1;
    display: flex;
    justify-content: center;
    align-items: flex-start;
    padding: 20px 0 40px;
}

.btn-secondary {
    padding: 10px 16px;
    border: 1px solid var(--border-color);
    background: var(--surface-color);
    border-radius: 6px;
    cursor: pointer;
    box-shadow: var(--shadow-soft);
}

.btn-danger {
    padding: 10px 16px;
    border: none;
    background: var(--danger-color);
    color: #fff;
    border-radius: 6px;
    cursor: pointer;
}

/* Responsive Design */
@media (max-width: 768px) {
    .btn {
        padding: 16px 20px;
        font-size: 20px;
        min-width: 180px;
    }

    .button-container {
        flex-direction: column;
    }

    .button-divider {
        display: none;
    }

    .hero-card {
        padding: 36px 24px;
        margin: 0 16px;
    }

    .hero-features {
        margin-bottom: 20px;
    }
}