:root {
    --bg-color: #f8f9fa;
    --card-bg: #ffffff;
    --text-main: #2d3436;
    --text-muted: #636e72;
    --accent-color: #0984e3;
    --error-color: #d63031;
    --border-color: #dfe6e9;
    --shadow: 0 10px 25px rgba(0,0,0,0.05);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-main);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
}

.container {
    width: 100%;
    max-width: 500px;
    text-align: center;
}

header {
    margin-bottom: 2rem;
}

header h1 {
    font-size: 2.5rem;
    font-weight: 800;
    margin-bottom: 0.5rem;
    letter-spacing: -1px;
}

header p {
    color: var(--text-muted);
    font-size: 1rem;
}

.converter-card {
    background: var(--card-bg);
    padding: 2.5rem;
    border-radius: 24px;
    box-shadow: var(--shadow);
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    border: 1px solid var(--border-color);
}

.input-group {
    display: flex;
    flex-direction: column;
    text-align: left;
    gap: 0.5rem;
}

.input-group label {
    font-size: 0.85rem;
    font-weight: 600;
    color: var(--text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
}

.input-group input {
    font-size: 1.25rem;
    padding: 12px 16px;
    border: 2px solid var(--border-color);
    border-radius: 12px;
    transition: all 0.2s ease;
    outline: none;
    color: var(--text-main);
    font-weight: 500;
}

.input-group input:focus {
    border-color: var(--accent-color);
    box-shadow: 0 0 0 4px rgba(9, 132, 227, 0.1);
}

.divider {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 40px;
}

.arrow {
    font-size: 1.5rem;
    color: var(--accent-color);
    font-weight: bold;
}

.error-message {
    margin-top: 1.5rem;
    padding: 12px;
    background: #fff5f5;
    color: var(--error-color);
    border-radius: 12px;
    font-size: 0.9rem;
    border: 1px solid rgba(214, 48, 49, 0.2);
}

.hidden {
    display: none;
}

footer {
    margin-top: 2rem;
    font-size: 0.85rem;
    color: var(--text-muted);
}

@media (max-width: 400px) {
    .converter-card {
        padding: 1.5rem;
    }
}