Try out Lion as base for button.

Much easier to customize, though not without its issues:
- Lion give us some stuff to handle validation, forms & input that I haven't looked into
- Slightly different mixin structure, I might be missing out on something
- Properties in extending class cause TypeScript error, but still work

api/js/etemplate/et2_core_inheritance.ts

@@ -260,7 +260,7 @@ export class ClassWithAttributes extends ClassWithInterfaces
  */
 
 type Constructor<T = {}> = new (...args: any[]) => T;
-export const Et2Widget = <T extends Constructor<LitElement>>(superClass: T) => {
+export const Et2Widget = <T extends Constructor>(superClass: T) => {
 	class Et2WidgetClass extends superClass implements et2_IDOMNode {
 
 		/** et2_widget compatability **/