feat: support for IE11 browser

frontend/src/main.js

@@ -1,3 +1,5 @@
+import "whatwg-fetch";
+import cssVars from "css-vars-ponyfill";
 import { sync } from "vuex-router-sync";
 import store from "@/store";
 import router from "@/router";
@@ -7,6 +9,8 @@ import { recaptcha, loginPage } from "@/utils/constants";
 import { login, validateLogin } from "@/utils/auth";
 import App from "@/App";
 
+cssVars();
+
 sync(store, router);
 
 async function start() {