    });
      let p_target = document.getElementById("p_target"),
        p_response = document.getElementById("p_response");
      p_target.addEventListener("keyup", e => {
        p_response.style.display =
          p_target.value === "1em" ? "block" : "none";
      });
      let bc_target = document.getElementById("bc_target"),
        bc_response = document.getElementById("bc_response");
      let bc_observer = new MutationObserver(mutations => {
        mutations.forEach(mutation => {
          bc_res