:root {
    --primary-color: #007AFF;
    --background-color: #F5F7F9;
    --card-background: #FFFFFF;
    --text-color: #1D1D1F;
    --border-color: #E0E0E0;
    --shadow: 0 4px 12px rgba(0, 0, 0, 0.08);
    --border-radius: 12px;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}

body {
    background-color: var(--background-color);
    color: var(--text-color);
    padding: 20px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

.container {
    width: 100%;
    max-width: 900px;
    margin: 0 auto;
}

header {
    text-align: center;
    margin-bottom: 30px;
}

h1 {
    font-weight: 600;
    font-size: 28px;
    margin-bottom: 8px;
}

.subtitle {
    color: #86868B;
    font-size: 16px;
}

.converter-card {
    background-color: var(--card-background);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: 25px;
    margin-bottom: 30px;
}

.units-container {
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
    margin-bottom: 25px;
}

.unit-section {
    flex: 1;
    min-width: 280px;
}

.section-title {
    font-size: 16px;
    font-weight: 500;
    margin-bottom: 15px;
    color: #86868B;
    padding-bottom: 8px;
    border-bottom: 1px solid var(--border-color);
}

.input-group {
    margin-bottom: 15px;
}

.input-group label {
    display: block;
    margin-bottom: 6px;
    font-size: 14px;
    font-weight: 500;
}

.input-field {
    width: 100%;
    padding: 12px 15px;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    font-size: 16px;
    transition: all 0.2s;
}

.input-field:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 2px rgba(0, 122, 255, 0.2);
}

.explanation {
    background-color: var(--card-background);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    padding: 25px;
}

.explanation h2 {
    font-size: 18px;
    font-weight: 600;
    margin-bottom: 15px;
}

.explanation p {
    margin-bottom: 15px;
    line-height: 1.5;
    font-size: 15px;
}

.highlight {
    color: var(--primary-color);
    font-weight: 500;
}

footer {
    margin-top: 30px;
    text-align: center;
    color: #86868B;
    font-size: 14px;
}

@media (max-width: 768px) {
    .units-container {
        flex-direction: column;
    }
    
    .converter-card, .explanation {
        padding: 20px;
    }
}