:root {
    --bg-color: #1a1a1a;
    --text-color: #f0f0f0;
    --primary-color: #4a90e2;
    --container-bg-color: #2c2c2c;
    --input-bg-color: #3a3a3a;
    --border-color: #444;
    --shadow-color: rgba(0, 0, 0, 0.2);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 1rem;
}

.converter-wrapper {
    width: 100%;
    max-width: 600px;
    background-color: var(--container-bg-color);
    border-radius: 12px;
    box-shadow: 0 10px 25px var(--shadow-color);
    overflow: hidden;
}

header {
    background-color: var(--primary-color);
    padding: 1.5rem;
    text-align: center;
}

header h1 {
    font-size: 1.8rem;
    font-weight: 600;
    color: #fff;
}

main {
    padding: 1.5rem;
}

.category-tabs {
    display: flex;
    justify-content: space-around;
    margin-bottom: 2rem;
    border-bottom: 1px solid var(--border-color);
}

.category-tabs button {
    flex-grow: 1;
    padding: 1rem 0.5rem;
    font-size: 1rem;
    font-weight: 500;
    background: none;
    border: none;
    color: var(--text-color);
    cursor: pointer;
    transition: background-color 0.3s, color 0.3s;
    border-bottom: 3px solid transparent;
}

.category-tabs button:hover {
    background-color: var(--input-bg-color);
}

.category-tabs button.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
}

.converter-body {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 1rem;
}

.equals-sign {
    font-size: 2rem;
    font-weight: bold;
    color: var(--primary-color);
}

.converter-group {
    flex: 1;
    display: flex;
    flex-direction: column;
    gap: 0.5rem;
}

.converter-group label {
    font-size: 0.9rem;
    color: #aaa;
}

input[type="number"],
select {
    width: 100%;
    padding: 0.8rem;
    background-color: var(--input-bg-color);
    border: 1px solid var(--border-color);
    border-radius: 6px;
    color: var(--text-color);
    font-size: 1.2rem;
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
}

select {
    background-image: url("data:image/svg+xml;charset=UTF-8,%3csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24' fill='none' stroke='%23f0f0f0' stroke-width='2' stroke-linecap='round' stroke-linejoin='round'%3e%3cpolyline points='6 9 12 15 18 9'%3e%3c/polyline%3e%3c/svg%3e");
    background-repeat: no-repeat;
    background-position: right 0.8rem center;
    background-size: 1em;
    padding-right: 2.5rem; /* Make space for arrow */
}

input[type="number"]:focus,
select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.3);
}

footer {
    text-align: center;
    padding: 1rem;
    font-size: 0.8rem;
    color: #888;
    border-top: 1px solid var(--border-color);
}

/* Responsive Design */
@media (max-width: 600px) {
    body {
        padding: 0;
        align-items: flex-start;
    }

    .converter-wrapper {
        border-radius: 0;
        min-height: 100vh;
    }

    .converter-body {
        flex-direction: column;
        gap: 1.5rem;
    }

    .equals-sign {
        transform: rotate(90deg);
    }

    header h1 {
        font-size: 1.5rem;
    }

    .category-tabs button {
        font-size: 0.9rem;
    }
}