:root {
    --primary: #0b7285;
    --background: #f8f9fa;
    --input-border: #ced4da;
    --input-focus: #74c0fc;
    --result-bg: #e3fafc;
    --result-text: #087f5b;
    --warning-bg: #fff3bf;
    --warning-text: #856404;
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    padding: 2rem 1.5rem;
    font-family: 'Roboto Mono', monospace;
    font-size: 1.1rem;
    background-color: var(--background);
    color: #212529;
}

h1 {
    font-size: 1.8rem;
    font-weight: 600;
    text-align: center;
    margin-bottom: 2.5rem;
    color: #111;
}

label {
    display: block;
    font-weight: 600;
    margin-bottom: 0.4rem;
}

input[type="number"] {
    width: 100%;
    padding: 1rem;
    font-size: 1.2rem;
    border: none;
    border-bottom: 2px solid var(--input-border);
    background-color: transparent;
    transition: border-color 0.25s;
}

input[type="number"]:focus {
    outline: none;
    border-bottom-color: var(--input-focus);
}

.field {
    margin-bottom: 2rem;
}

.banknote-buttons {
    display: flex;
    flex-wrap: wrap;
    gap: 0.75rem;
    margin-top: 0.5rem;
}

.banknote-buttons button {
    flex: 1 1 calc(25% - 0.75rem);
    padding: 0.75rem 0;
    font-size: 1rem;
    font-weight: 600;
    background-color: #f1f3f5;
    color: #212529;
    border: none;
    border-radius: 0;
    cursor: pointer;
    transition: all 0.2s ease;
}

.banknote-buttons button:hover {
    background-color: #e3fafc;
    color: #087f5b;
}

.result {
    margin-top: 2rem;
    padding: 1.5rem 1rem;
    font-size: 1.5rem;
    font-weight: 600;
    text-align: center;
    background: var(--result-bg);
    color: var(--result-text);
    display: none;
}

.result small {
    display: block;
    font-size: 0.9rem;
    margin-top: 0.5rem;
    font-weight: 400;
    color: #495057;
}

.result.warning {
    background: var(--warning-bg);
    color: var(--warning-text);
}

@media (min-width: 600px) {
    body {
        max-width: 480px;
        margin: auto;
    }
}

.actions {
    text-align: center;
    margin-top: 1.5em;
}

.clear-btn {
    background: #e74c3c;
    color: #fff;
    border: none;
    padding: 0.6em 1.2em;
    font-family: 'Roboto Mono', monospace;
    font-size: 1em;
    border-radius: 8px;
    cursor: pointer;
    transition: background 0.2s ease;
}

.clear-btn:hover {
    background: #c0392b;
}

.clear-btn:active {
    background: #a93226;
}

.clear-btn {
    display: none;
}