message: Add a function to get the "base" theme for a theme
  Useful for trying to load the right assets first.
  See
diff: @@ -60,6 +60,22 @@ function getCustomTheme(themeName) {
  return customTheme;
  }
  +/**
  + * Gets the underlying theme name for the given theme. This is usually the theme or
  + * CSS resource that the theme relies upon to load.
  + * @param {string} theme The theme name to get the base of.
  + * @returns {string} The base theme (typically "light" or "dark").
  + */
  +export function getBaseTheme(theme) {
  + if (!theme) return "light";
  + if (theme.startsWith("custom-")) {
  + const customTheme = getCustomTheme(theme.substr(7));
  + return customTheme.is_dark ? "dark-custom" : "light-custom";
  + }
  +
  + return theme; // it's probably a base theme
  +}
  +
  /**
  * Called whenever someone changes the theme
  *
  