Function preview

frontend/src/ts/controllers/theme-controller.ts:123–129

(
  themeIdentifier: ThemeIdentifier,
  customColorsOverride?: CustomThemeColors,
)

let previewState: PreviewState = null;

export function preview(
  themeIdentifier: ThemeIdentifier,
  customColorsOverride?: CustomThemeColors,
): void {
  previewState = { theme: themeIdentifier, colors: customColorsOverride };
  debouncedPreview();
}

const debouncedPreview = debounce<() => void>(250, () => {
  if (previewState) {