: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: #e2e8f0;
    --shadow: 0 10px 25px -5px rgba(0, 0, 0, 0.1), 0 8px 10px -6px rgba(0, 0, 0, 0.1);
}

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

body {
    font-family: 'Inter', 'Noto Sans JP', sans-serif;
    background: var(--bg-gradient);
    color: var(--text-main);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    line-height: 1.6;
}

.container {
    width: 100%;
    max-width: 1000px;
    padding: 2rem;
}

header {
    text-align: center;
    margin-bottom: 3rem;
}

header h1 {
    font-size: 2.5rem;
    font-weight: 700;
    background: linear-gradient(to right, #6366f1, #a855f7);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    margin-bottom: 0.5rem;
}

.subtitle {
    color: var(--text-muted);
    font-size: 1.1rem;
}

.calculator-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2.5rem;
}

.card {
    background: var(--card-bg);
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.3);
    border-radius: 1.5rem;
    padding: 2rem;
    box-shadow: var(--shadow);
    transition: transform 0.3s ease;
}

.card:hover {
    transform: translateY(-5px);
}

h2 {
    font-size: 1.25rem;
    margin-bottom: 1.5rem;
    padding-bottom: 0.75rem;
    border-bottom: 2px solid var(--border-color);
    color: var(--primary-color);
}

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

label {
    display: block;
    font-weight: 600;
    margin-bottom: 0.5rem;
    font-size: 0.9rem;
    color: var(--text-muted);
}

.input-wrapper, .output-wrapper {
    position: relative;
    display: flex;
    align-items: center;
}

input {
    width: 100%;
    padding: 0.75rem 1rem;
    border: 1.5px solid var(--border-color);
    border-radius: 0.75rem;
    font-size: 1rem;
    outline: none;
    transition: all 0.2s ease;
}

input:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(99, 102, 241, 0.2);
}

input[readonly] {
    background-color: #f1f5f9;
    cursor: default;
}

.unit {
    position: absolute;
    right: 1rem;
    color: var(--text-muted);
    font-size: 0.9rem;
    pointer-events: none;
}

.copy-btn {
    position: absolute;
    right: 0.5rem;
    background: white;
    border: 1px solid var(--border-color);
    border-radius: 0.5rem;
    padding: 0.4rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    color: var(--text-muted);
    transition: all 0.2s ease;
}

.copy-btn:hover {
    color: var(--primary-color);
    border-color: var(--primary-color);
    background: #f5f3ff;
}

.copy-btn:active {
    transform: scale(0.95);
}

footer {
    margin-top: 3rem;
    text-align: center;
    color: var(--text-muted);
    font-size: 0.85rem;
}

/* Response for Mobile */
@media (max-width: 768px) {
    .calculator-grid {
        grid-template-columns: 1fr;
    }
    
    .container {
        padding: 1rem;
    }
    
    header h1 {
        font-size: 2rem;
    }
}