abtmtr-v4/views/scripts/interface.js

function propagateStyles(rootStyles, parent) {
  if (parent == null && window.frameElement == null) return;
  const wfParent = parent ?? window.frameElement.parentElement;
  wfParent.style.setProperty(
    "--base-color",
    rootStyles.getPropertyValue("--base-color")
  );
}

window.addEventListener("DOMContentLoaded", () => {
  propagateStyles(getComputedStyle(document.documentElement));
});