Text buttons use opacity for hover

This allows a text button to look appropriate in the App Bar when hovering over it, while still retaining desired hover behavior elsewhere by the UX design team.

I sourced the implementation from IconButton, since the hamburger menu icon in my app was behaving as desired.

src/overrides/buttons.js

 import defaultTheme from "../defaultTheme";
 import { colorBlueHover, colorGrayHover, colorGrayLight } from "../colors";
+import {fade} from '@material-ui/core/styles/colorManipulator';
+
 
 const containedOverrides = {
   "&:hover": {
@@ -26,7 +28,7 @@ const outlinedOverrides = {
 
 const textOverrides = {
   "&:hover": {
-    backgroundColor: colorGrayHover,
+    backgroundColor: fade(defaultTheme.palette.action.active, defaultTheme.palette.action.hoverOpacity)
   },
   "&:disabled": {
     color: colorGrayLight,