:root {
    --primary: #2c3e50;
    --accent: #3498db;
    --error: #e74c3c;
    --bg: #f8f9fa;
    --text: #333;
    --white: #ffffff;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    line-height: 1.6;
    color: var(--text);
    background-color: var(--bg);
    padding: 20px;
}

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

h1 {
    color: var(--primary);
    margin-bottom: 10px;
}

#app {
    max-width: 600px;
    margin: 0 auto;
    background: var(--white);
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}

.input-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 15px;
    margin-bottom: 20px;
}

.input-group {
    display: flex;
    flex-direction: column;
}

label {
    font-weight: bold;
    margin-bottom: 5px;
    font-size: 0.9rem;
}

input {
    padding: 10px;
    border: 1px solid #ddd;
    border-radius: 4px;
    font-size: 1rem;
}

.actions {
    display: flex;
    gap: 10px;
}

button {
    flex: 1;
    padding: 12px;
    border: none;
    border-radius: 4px;
    cursor: pointer;
    font-weight: bold;
    transition: background 0.3s;
}

#btn-calculate {
    background-color: var(--accent);
    color: var(--white);
}

#btn-calculate:hover {
    background-color: #2980b9;
}

#btn-reset {
    background-color: #eee;
    color: var(--text);
}

.hidden {
    display: none;
}

.error {
    margin-top: 20px;
    padding: 15px;
    background-color: #f8d7da;
    color: #721c24;
    border-radius: 4px;
    border: 1px solid #f5c6cb;
}

#results {
    margin-top: 30px;
    border-top: 2px solid #eee;
    padding-top: 20px;
}

@media (max-width: 480px) {
    .input-grid {
        grid-template-columns: 1fr;
    }
}