:root {
    --bg: #f7f9fc;
    --card: #ffffff;
    --border: #d8dee9;
    --text: #2d3748;
    --muted: #718096;
    --primary: #2563eb;
    --primary-hover: #1d4ed8;
    --accent: #16a34a;
    --shadow: 0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
}

* { box-sizing: border-box; }

body {
    margin: 0;
    padding: 0;
    background: var(--bg);
    color: var(--text);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    line-height: 1.5;
}

header {
    background: linear-gradient(135deg, #1e3a8a 0%, #2563eb 100%);
    color: white;
    padding: 32px 24px;
    text-align: center;
}

header h1 {
    margin: 0;
    font-size: 28px;
    font-weight: 600;
}

header .subtitle {
    margin: 6px 0 2px;
    opacity: 0.9;
    font-size: 14px;
}

header .byline {
    margin: 2px 0 0;
    opacity: 0.8;
    font-size: 13px;
}

main {
    max-width: 920px;
    margin: 24px auto;
    padding: 0 16px;
}

.intro {
    background: var(--card);
    border: 1px solid var(--border);
    padding: 14px 18px;
    border-radius: 8px;
    box-shadow: var(--shadow);
    color: var(--muted);
    font-size: 14px;
    margin-bottom: 20px;
}

fieldset {
    background: var(--card);
    border: 1px solid var(--border);
    border-radius: 8px;
    padding: 16px 20px 20px;
    margin: 0 0 18px;
    box-shadow: var(--shadow);
}

legend {
    padding: 0 8px;
    font-weight: 600;
    color: var(--primary);
    font-size: 14px;
    text-transform: uppercase;
    letter-spacing: 0.04em;
}

.grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
    gap: 12px 16px;
}

.checkbox-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 6px 16px;
    margin-bottom: 12px;
}

label {
    display: flex;
    flex-direction: column;
    font-size: 13px;
    font-weight: 500;
    color: var(--muted);
}

.checkbox-grid label {
    flex-direction: row;
    align-items: center;
    color: var(--text);
    font-weight: 400;
    cursor: pointer;
}

.checkbox-grid input[type="checkbox"] {
    margin-right: 8px;
    transform: scale(1.1);
}

input[type="number"], select {
    margin-top: 4px;
    padding: 7px 10px;
    border: 1px solid var(--border);
    border-radius: 6px;
    font-size: 14px;
    color: var(--text);
    background: white;
    transition: border-color 0.15s;
}

input[type="number"]:focus, select:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(37,99,235,0.15);
}

button {
    width: 100%;
    padding: 13px;
    background: var(--primary);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 15px;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.15s;
}

button:hover:not(:disabled) {
    background: var(--primary-hover);
}

button:disabled {
    background: #94a3b8;
    cursor: not-allowed;
}

#result {
    background: var(--card);
    border: 1px solid var(--accent);
    border-left: 4px solid var(--accent);
    padding: 22px 24px;
    border-radius: 8px;
    box-shadow: var(--shadow);
    margin: 22px 0;
    text-align: center;
}

#result h2 {
    margin: 0 0 10px;
    font-size: 14px;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--muted);
    font-weight: 500;
}

#result-amount {
    font-size: 38px;
    font-weight: 700;
    color: var(--accent);
    margin: 4px 0 6px;
    letter-spacing: -0.02em;
}

.muted {
    color: var(--muted);
    font-size: 13px;
    margin: 4px 0;
}

#status {
    text-align: center;
    margin: 16px 0;
}

footer {
    max-width: 920px;
    margin: 8px auto 32px;
    padding: 0 24px;
    text-align: center;
}