getStyle doesn't work

export const config: PlasmoContentScript = {...};

export const getStyle: PlasmoGetStyle () => {
  const elStyle = document.createElement("style");
  elStyle.textContent = `
    .iframe-bst {
      width: 100%;
      height: 500px;
      background-color: white;
    }
`;
  return elStyle;
};

const elIframe = document.createElement("iframe");
elIframe.src = "";
elIframe.classList.add("iframe-bst");

const elParent = document.querySelector(".selector");
elParent.append(elIframe);