🐛 Adds text/css type attr for custom stylesheets (#560)

Author: Lissy93

src/utils/ThemeHelper.js

@@ -32,6 +32,7 @@ export const LoadExternalTheme = function th() {
   const preloadTheme = (href) => {
     const link = document.createElement('link');
     link.rel = 'stylesheet';
+    link.type = 'text/css'
     link.href = href;
     document.head.appendChild(link);
     return new Promise((resolve, reject) => {