:root {
    --bg-color: #f4f7f9;
    --card-bg: #ffffff;
    --text-color: #333333;
    --primary-color: #3498db;
    --secondary-color: #95a5a6;
    --border-color: #e0e0e0;
    --accent-color: #2ecc71;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

[data-theme="dark"] {
    --bg-color: #1a1a1a;
    --card-bg: #2d2d2d;
    --text-color: #f4f7f9;
    --primary-color: #3498db;
    --secondary-color: #7f8c8d;
    --border-color: #444444;
    --accent-color: #2ecc71;
    --shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
}

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

body {
    font-family: 'Sarabun', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    padding: 20px;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    width: 100%;
    max-width: 450px;
}

.card {
    background-color: var(--card-bg);
    padding: 30px;
    border-radius: 12px;
    box-shadow: var(--shadow);
    transition: background-color 0.3s ease;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: 25px;
}

h1 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 5px;
}

.subtitle {
    font-size: 0.9rem;
    color: var(--secondary-color);
}

#theme-toggle {
    background: none;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 8px;
    cursor: pointer;
    font-size: 1.2rem;
    color: var(--text-color);
    transition: all 0.2s ease;
}

#theme-toggle:hover {
    background-color: var(--border-color);
}

.form-group {
    margin-bottom: 20px;
}

.form-group.hidden {
    display: none;
}

label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    font-size: 0.9rem;
}

input, select {
    width: 100%;
    padding: 12px;
    border: 1px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    background-color: var(--card-bg);
    color: var(--text-color);
    transition: border-color 0.2s ease;
}

input:focus, select:focus {
    outline: none;
    border-color: var(--primary-color);
}

.hint {
    font-size: 0.8rem;
    color: var(--secondary-color);
    margin-bottom: 25px;
    font-style: italic;
}

.actions {
    margin-bottom: 30px;
}

button {
    cursor: pointer;
    font-size: 1rem;
    font-weight: 600;
    padding: 10px 20px;
    border-radius: 8px;
    transition: background-color 0.2s ease;
}

.btn-secondary {
    background: none;
    border: 1px solid var(--border-color);
    color: var(--secondary-color);
    width: 100%;
}

.btn-secondary:hover {
    background-color: var(--border-color);
    color: var(--text-color);
}

.results {
    border-top: 1px solid var(--border-color);
    padding-top: 25px;
}

.result-item {
    display: flex;
    justify-content: space-between;
    margin-bottom: 10px;
    font-size: 0.95rem;
}

.result-total {
    margin-top: 20px;
    text-align: center;
}

.result-total label {
    font-size: 0.85rem;
    text-transform: uppercase;
    letter-spacing: 1px;
    color: var(--secondary-color);
}

#res-total-pay {
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--primary-color);
}

@media (max-width: 480px) {
    .card {
        padding: 20px;
    }
}