[improvement] Error class invade color usage rule.

## Subject

Color should be used in background.

/home/user/w/css/css/field-label.css:32-40

```css
p[data-type="error"] {
    display: block;
    margin: 0.5rem 0 0 0;
    color: rgb(var(--rgb-error));
    font-size: var(--md-font-size);
    line-height: var(--md-line-height);
    font-family: var(--font-family-sans);
    letter-spacing: var(--md-letter-spacing);
}
```