wagtail/client/scss/components/forms/_input-base.scss

/**
 * Field styles reusable across **all** fields, including:
 * Text input, textarea, checkbox, radio, select, etc.
 */
@mixin input-base() {
  @include more-contrast-interactive();
  appearance: none;
  border-radius: theme('borderRadius.DEFAULT');
  color: theme('colors.text-context');
  background-color: theme('colors.surface-field');
  border: 1px solid theme('colors.border-field-default');

  &:hover {
    border-color: theme('colors.border-field-hover');
  }

  &[disabled],
  &[disabled]:hover {
    color: theme('colors.text-placeholder');
    background-color: theme('colors.surface-field-inactive');
    border-color: theme('colors.border-field-inactive');
    cursor: not-allowed;
  }

  // Only show the error state for the specific field in error.
  .w-field--error > .w-field__input > &,
  // Allow for one wrapper level within StreamField.
  .w-field--error > .w-field__input > * > &,
  // Ideally, individual widgets should show they are in error state with aria-invalid.
  &[aria-invalid='true'] {
    border-color: theme('colors.critical.200');
  }

  &::placeholder {
    color: theme('colors.text-placeholder');
  }
}