:root {
    --primary-color: #4f46e5;
    --secondary-color: #6366f1;
    --text-color: #1f2937;
    --bg-color: #f9fafb;
    --accent-color: #10b981;
    --error-color: #ef4444;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
}

body {
    font-family: 'Inter', sans-serif;
    background: linear-gradient(to bottom right, #e0e7ff, #f3e8ff);
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    color: var(--text-color);
}

.container {
    background: white;
    padding: 2.5rem;
    border-radius: 1rem;
    box-shadow: var(--shadow);
    max-width: 28rem;
    width: 100%;
}

.header {
    display: flex;
    align-items: center;
    justify-content: center;
    margin-bottom: 2rem;
}

.header i {
    font-size: 1.5rem;
    color: var(--primary-color);
    margin-right: 0.75rem;
}

h1 {
    font-size: 1.875rem;
    font-weight: 700;
    margin: 0;
}

label {
    display: block;
    font-size: 0.875rem;
    font-weight: 500;
    margin-bottom: 0.5rem;
}

select, input {
    width: 100%;
    padding: 0.75rem 1rem;
    margin-bottom: 1.25rem;
    border: 1px solid #d1d5db;
    border-radius: 0.5rem;
    font-size: 1rem;
    background-color: #ffffff;
    transition: border-color 0.15s ease-in-out, box-shadow 0.15s ease-in-out;
}

select:focus, input:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(79, 70, 229, 0.1);
    outline: none;
}

button {
    width: 100%;
    padding: 0.75rem 1rem;
    font-size: 1rem;
    font-weight: 600;
    color: white;
    background: linear-gradient(to right, var(--primary-color), var(--secondary-color));
    border: none;
    border-radius: 0.5rem;
    cursor: pointer;
    transition: transform 0.1s ease, box-shadow 0.1s ease;
}

button:hover {
    transform: translateY(-1px);
    box-shadow: 0 4px 6px -1px rgba(79, 70, 229, 0.3);
}

#resultados {
    margin-top: 1.5rem;
    padding: 1.25rem;
    background: var(--bg-color);
    border-radius: 0.5rem;
    font-size: 1rem;
    line-height: 1.5;
}

#resultados strong {
    color: var(--error-color);
}

.result-item {
    display: flex;
    justify-content: space-between;
    margin-bottom: 0.5rem;
}

.result-item:last-child {
    margin-bottom: 0;
}

.neto {
    color: var(--accent-color);
    font-weight: 600;
}

.diferencia {
    margin-top: 1rem;
    font-style: italic;
}

.donation-banner {
    position: fixed;
    bottom: 20px;
    right: 20px;
    background: white;
    padding: 10px 15px;
    border-radius: 5px;
    box-shadow: var(--shadow);
    font-size: 0.875rem;
    font-weight: 500;
    z-index: 1000;
}

.donation-banner a {
    color: var(--primary-color);
    text-decoration: none;
    display: flex;
    align-items: center;
    gap: 5px;
}

.donation-banner a:hover {
    color: var(--secondary-color);
}

@media (max-width: 640px) {
    .container {
        padding: 1.5rem;
        margin: 1rem;
    }

    h1 {
        font-size: 1.5rem;
    }
}