:root {
    --primary-color: #2563eb;
    --primary-hover: #1d4ed8;
    --bg-color: #f8fafc;
    --surface-color: #ffffff;
    --text-color: #1e293b;
    --text-secondary: #64748b;
    --border-color: #e2e8f0;
    --card-shadow: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --container-width: 1000px;
    --radius: 12px;
}

[data-theme="dark"] {
    --primary-color: #3b82f6;
    --primary-hover: #60a5fa;
    --bg-color: #0f172a;
    --surface-color: #1e293b;
    --text-color: #f1f5f9;
    --text-secondary: #94a3b8;
    --border-color: #334155;
    --card-shadow: 0 10px 15px -3px rgb(0 0 0 / 0.5);
}

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

body {
    font-family: 'Pretendard', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    transition: background-color 0.3s, color 0.3s;
}

.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 0 20px;
}

/* Header & Nav */
header {
    background-color: var(--surface-color);
    border-bottom: 1px solid var(--border-color);
    padding: 1rem 0;
    position: sticky;
    top: 0;
    z-index: 100;
}

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

.logo {
    font-size: 1.5rem;
    font-weight: 700;
}

.logo span {
    color: var(--primary-color);
}

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

.nav-links a {
    text-decoration: none;
    color: var(--text-color);
    font-weight: 500;
    transition: color 0.2s;
}

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

/* Dropdown */
.dropdown {
    position: relative;
}

.dropdown-menu {
    position: absolute;
    top: 100%;
    left: 0;
    background-color: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    list-style: none;
    padding: 0.5rem 0;
    min-width: 200px;
    box-shadow: var(--card-shadow);
    display: none;
}

.dropdown:hover .dropdown-menu {
    display: block;
}

.dropdown-menu li a {
    padding: 0.5rem 1rem;
    display: block;
    font-size: 0.9rem;
}

.dropdown-menu li a:hover {
    background-color: var(--bg-color);
}

/* Hero */
.hero {
    text-align: center;
    padding: 4rem 0;
}

.hero h2 {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.hero p {
    color: var(--text-secondary);
    font-size: 1.1rem;
}

/* Calc Grid */
.calc-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.5rem;
    margin-bottom: 4rem;
}

.calc-card {
    background-color: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 2rem;
    cursor: pointer;
    transition: transform 0.2s, box-shadow 0.2s;
    text-align: center;
}

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

.calc-card .icon {
    font-size: 2.5rem;
    margin-bottom: 1rem;
}

.calc-card h3 {
    margin-bottom: 0.5rem;
}

.calc-card p {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

/* View Management */
.view {
    display: none;
}

.view.active {
    display: block;
}

/* Calc View */
.calc-header {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin: 2rem 0;
}

.back-btn {
    background: none;
    border: 1px solid var(--border-color);
    padding: 0.5rem 1rem;
    border-radius: var(--radius);
    cursor: pointer;
    color: var(--text-color);
}

.calc-container {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    background-color: var(--surface-color);
    border: 1px solid var(--border-color);
    border-radius: var(--radius);
    padding: 2rem;
    margin-bottom: 4rem;
}

.calc-inputs {
    border-right: 1px solid var(--border-color);
    padding-right: 2rem;
}

.input-group {
    margin-bottom: 1.5rem;
}

.input-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
}

.input-group input, .input-group select {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    background-color: var(--bg-color);
    color: var(--text-color);
    font-size: 1rem;
}

.calc-btn {
    width: 100%;
    padding: 1rem;
    background-color: var(--primary-color);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    margin-top: 1rem;
}

.calc-btn:hover {
    background-color: var(--primary-hover);
}

.result-item {
    background-color: var(--bg-color);
    padding: 1rem;
    border-radius: 8px;
    margin-bottom: 1rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.result-label {
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.result-value {
    font-weight: 700;
    font-size: 1.2rem;
    color: var(--primary-color);
}

.placeholder-msg {
    text-align: center;
    color: var(--text-secondary);
    padding: 4rem 0;
}

/* Footer */
footer {
    text-align: center;
    padding: 2rem 0;
    border-top: 1px solid var(--border-color);
    color: var(--text-secondary);
    font-size: 0.9rem;
}

@media (max-width: 768px) {
    .calc-container {
        grid-template-columns: 1fr;
    }
    .calc-inputs {
        border-right: none;
        padding-right: 0;
        border-bottom: 1px solid var(--border-color);
        padding-bottom: 2rem;
    }
}