:root {
    --primary-color: #0f172a;
    --accent-blue: #2563eb;
    --accent-orange: #ea580c;
    --accent-green: #059669;
    --bg-color: #f8fafc;
    --text-color: #334155;
    --container-bg: #ffffff;
    --border-color: #e2e8f0;
    --nav-bg: #ffffff;
    --footer-bg: #f1f5f9;
    --card-bg: #ffffff;
    --input-bg: #ffffff;
    --result-bg: #f0f9ff;
    --result-border: #bae6fd;
    --disclaimer-bg: #f8fafc;
}

body.dark-mode {
    --primary-color: #f1f5f9;
    --bg-color: #020617;
    --text-color: #cbd5e1;
    --container-bg: #1e293b;
    --border-color: #334155;
    --nav-bg: #0f172a;
    --footer-bg: #020617;
    --card-bg: #1e293b;
    --input-bg: #0f172a;
    --result-bg: #0c1a2e;
    --result-border: #1e3a5f;
    --disclaimer-bg: #1e293b;
}

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

body {
    font-family: 'Apple SD Gothic Neo', 'Malgun Gothic', 'Noto Sans KR', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.7;
    transition: background-color 0.3s, color 0.3s;
}

/* ===== NAVIGATION ===== */
nav {
    background-color: var(--nav-bg);
    border-bottom: 1px solid var(--border-color);
    padding: 0 20px;
    height: 70px;
    display: flex;
    align-items: center;
    justify-content: space-between;
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: 0 2px 4px rgba(0,0,0,0.02);
}

.logo {
    font-size: 20px;
    font-weight: 800;
    color: var(--primary-color);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 8px;
}

.nav-right {
    display: flex;
    align-items: center;
    gap: 20px;
}

.nav-links {
    display: flex;
    gap: 25px;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-color);
    font-weight: 600;
    font-size: 15px;
    transition: color 0.2s;
}

.nav-links a:hover, .nav-links a.active {
    color: var(--accent-blue);
}

.toggle-group {
    display: flex;
    gap: 10px;
    border-left: 1px solid var(--border-color);
    padding-left: 20px;
}

.toggle-btn {
    background: none;
    border: 1px solid var(--border-color);
    color: var(--text-color);
    padding: 6px 12px;
    border-radius: 20px;
    cursor: pointer;
    font-size: 13px;
    font-weight: 600;
    transition: all 0.2s;
}

.toggle-btn:hover {
    background: var(--bg-color);
    border-color: var(--accent-blue);
}

/* ===== HERO (INDEX) ===== */
.hero {
    text-align: center;
    padding: 80px 20px;
}
.hero h1 { font-size: 36px; color: var(--primary-color); margin-bottom: 20px; }
.hero p { font-size: 18px; color: #64748b; max-width: 700px; margin: 0 auto; }

/* ===== CONTAINER ===== */
.container {
    max-width: 1000px;
    margin: 40px auto;
    padding: 0 20px;
}

/* ===== CARDS (INDEX) ===== */
.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 30px;
    margin-bottom: 80px;
}
.card {
    background: var(--card-bg);
    border-radius: 20px;
    padding: 40px 30px;
    text-decoration: none;
    color: inherit;
    border: 1px solid var(--border-color);
    transition: all 0.3s;
    text-align: center;
}
.card:hover { transform: translateY(-8px); border-color: var(--accent-blue); }
.card-icon { font-size: 48px; margin-bottom: 20px; }
.card h2 { color: var(--primary-color); margin-bottom: 12px; }
.card p { font-size: 15px; color: #64748b; margin-bottom: 20px; }

/* ===== CALC SECTION ===== */
.calc-section {
    background: var(--container-bg);
    padding: 40px;
    border-radius: 20px;
    border: 1px solid var(--border-color);
    margin-bottom: 50px;
}
.calc-section h1 { text-align: center; margin-bottom: 30px; color: var(--primary-color); }

.form-group { margin-bottom: 20px; }
label { display: block; font-weight: 700; margin-bottom: 8px; color: var(--primary-color); }
input, select {
    width: 100%; padding: 12px; border: 1px solid var(--border-color); border-radius: 8px;
    background: var(--input-bg); color: var(--text-color); font-size: 16px;
}
.grid-2 { display: grid; grid-template-columns: 1fr 1fr; gap: 20px; }

.calc-btn {
    width: 100%; padding: 15px; border-radius: 10px; border: none; font-weight: 800; font-size: 17px; cursor: pointer; color: white;
}
.btn-blue { background: var(--accent-blue); }
.btn-orange { background: var(--accent-orange); }

.result-box {
    display: none; margin-top: 30px; padding: 25px; border-radius: 12px;
    background: var(--result-bg); border: 1px solid var(--result-border);
}
.result-row { display: flex; justify-content: space-between; margin-bottom: 10px; }
.result-total {
    margin-top: 15px; padding-top: 15px; border-top: 1px dashed var(--result-border);
    display: flex; justify-content: space-between; font-weight: 800; font-size: 20px;
}
.disclaimer {
    margin-top: 20px; font-size: 13px; color: #64748b; padding: 12px;
    background: var(--disclaimer-bg); border-radius: 8px; text-align: center; border: 1px solid var(--border-color);
}

/* ===== ARTICLE ===== */
article {
    background: var(--container-bg); padding: 50px; border-radius: 20px; border: 1px solid var(--border-color); margin-bottom: 50px;
}
article h2 { margin: 30px 0 20px; border-left: 5px solid var(--accent-blue); padding-left: 15px; color: var(--primary-color); }
article h3 { margin: 25px 0 10px; color: var(--primary-color); }
article p { margin-bottom: 15px; }
article ul, article ol { margin-bottom: 20px; padding-left: 20px; }
article li { margin-bottom: 8px; }

/* ===== VIDEO ===== */
.video-placeholder {
    width: 100%; aspect-ratio: 16/9; background: #000; border-radius: 12px;
    display: flex; align-items: center; justify-content: center; color: white; margin-top: 20px;
}

/* ===== FOOTER ===== */
footer {
    background-color: var(--footer-bg); padding: 50px 20px; text-align: center; border-top: 1px solid var(--border-color);
}
.footer-links { display: flex; justify-content: center; gap: 20px; margin-bottom: 20px; flex-wrap: wrap; }
.footer-links a { text-decoration: none; color: #64748b; font-size: 14px; }
.copyright { color: #94a3b8; font-size: 13px; }

/* ===== RESPONSIVE ===== */
@media (max-width: 768px) {
    .nav-links, .logo span { display: none; }
    .hero h1 { font-size: 26px; }
    article { padding: 30px 20px; }
}