:root {
    --primary-color: #6366f1;
    --primary-hover: #4f46e5;
    --bg-gradient: linear-gradient(135deg, #f8fafc 0%, #e2e8f0 100%);
    --card-bg: rgba(255, 255, 255, 0.8);
    --text-main: #1e293b;
    --text-muted: #64748b;
    --border-color: rgba(226, 232, 240, 0.8);
    --glass-shadow: 0 8px 32px 0 rgba(31, 38, 135, 0.07);
}

[data-theme="dark"] {
    --primary-color: #818cf8;
    --primary-hover: #6366f1;
    --bg-gradient: linear-gradient(135deg, #0f172a 0%, #1e293b 100%);
    --card-bg: rgba(30, 41, 59, 0.7);
    --text-main: #f8fafc;
    --text-muted: #94a3b8;
    --border-color: rgba(51, 65, 85, 0.8);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Outfit', 'Pretendard', -apple-system, BlinkMacSystemFont, system-ui, sans-serif;
}

/* Mobile Optimization & Fluid Typography */
body {
    background: var(--bg-gradient);
    background-attachment: fixed;
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    color: var(--text-main);
    padding: 16px; /* Reduced for mobile */
}

.container {
    width: 100%;
    max-width: 1100px;
    display: flex;
    justify-content: center;
    align-items: center;
}

.calculator-card {
    background: var(--card-bg);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    border-radius: 28px; /* Slightly rounder */
    border: 1px solid var(--border-color);
    box-shadow: var(--glass-shadow);
    padding: 40px;
    width: 100%;
    max-width: 550px;
    animation: fadeIn 0.6s cubic-bezier(0.16, 1, 0.3, 1);
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(30px); }
    to { opacity: 1; transform: translateY(0); }
}

h1 {
    font-size: clamp(1.5rem, 5vw, 2.2rem); /* Fluid font size */
    font-weight: 800;
    margin-bottom: 32px;
    text-align: center;
    background: linear-gradient(135deg, var(--primary-color), #ec4899);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    line-height: 1.2;
}

.input-group {
    margin-bottom: 20px;
}

label {
    display: block;
    font-size: 0.85rem;
    font-weight: 600;
    margin-bottom: 10px;
    color: var(--text-muted);
    padding-left: 4px;
}

input, select {
    width: 100%;
    padding: 16px 20px; /* Larger touch targets */
    border-radius: 16px;
    border: 1px solid var(--border-color);
    background: rgba(255, 255, 255, 0.4);
    color: var(--text-main);
    font-size: 1rem;
    transition: all 0.25s ease;
    outline: none;
    -webkit-appearance: none; /* Reset for iOS */
}

[data-theme="dark"] input, [data-theme="dark"] select {
    background: rgba(15, 23, 42, 0.4);
}

input:focus, select:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 4px rgba(99, 102, 241, 0.15);
    background: var(--card-bg);
}

button {
    width: 100%;
    padding: 18px;
    border-radius: 16px;
    border: none;
    background: var(--primary-color);
    color: white;
    font-size: 1.1rem;
    font-weight: 700;
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    margin-top: 12px;
    box-shadow: 0 10px 15px -3px rgba(99, 102, 241, 0.3);
}

button:hover {
    background: var(--primary-hover);
    transform: translateY(-2px);
    box-shadow: 0 20px 25px -5px rgba(99, 102, 241, 0.4);
}

button:active {
    transform: scale(0.98);
}

.result-section {
    margin-top: 40px;
    display: none;
    overflow-x: auto; /* Handle wide tables on small screens */
    scrollbar-width: none; /* Hide scrollbar for clean UI */
}

.result-section::-webkit-scrollbar {
    display: none;
}

.result-section.active {
    display: block;
    animation: slideUp 0.5s ease-out;
}

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

table {
    width: 100%;
    border-collapse: separate;
    border-spacing: 0;
    margin-top: 10px;
    border-radius: 20px;
    overflow: hidden;
    border: 1px solid var(--border-color);
    background: rgba(255, 255, 255, 0.05);
}

th {
    background: rgba(99, 102, 241, 0.08);
    color: var(--primary-color);
    font-weight: 700;
    text-transform: uppercase;
    font-size: 0.75rem;
    letter-spacing: 0.1em;
    padding: 18px 16px;
    text-align: left;
}

td {
    padding: 18px 16px;
    border-bottom: 1px solid var(--border-color);
    font-size: 0.95rem;
}

tr:last-child td {
    border-bottom: none;
}

.theme-toggle {
    position: fixed;
    top: 16px;
    right: 16px;
    background: var(--card-bg);
    backdrop-filter: blur(8px);
    border: 1px solid var(--border-color);
    width: 48px;
    height: 48px;
    border-radius: 50%; /* Circle for better UI */
    cursor: pointer;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.2rem;
    transition: all 0.3s ease;
    z-index: 1000;
    box-shadow: 0 4px 12px rgba(0,0,0,0.1);
}

@media (max-width: 480px) {
    body {
        padding: 12px;
        align-items: flex-start; /* Better for long content on mobile */
        padding-top: 80px;
    }

    .calculator-card {
        padding: 28px 20px;
        border-radius: 24px;
    }

    h1 {
        margin-bottom: 24px;
    }

    input, select, button {
        padding: 14px 16px;
        font-size: 0.95rem;
    }
    
    td, th {
        padding: 14px 12px;
        font-size: 0.85rem;
    }
}