Rollup merge of rust-lang#75901 - GuillaumeGomez:ayu-theme-button-hov…

…er-background-color, r=pickfire

Improve theme button hover background color

Fixes rust-lang#75880.

![Screenshot from 2020-08-25 13-44-01](https://user-images.githubusercontent.com/3050060/91170922-e60b1880-e6d9-11ea-9eb1-61a44cdc28d9.png)
![Screenshot from 2020-08-25 13-43-43](https://user-images.githubusercontent.com/3050060/91170924-e73c4580-e6d9-11ea-969e-616bf4130975.png)

r? @pickfire

src/librustdoc/html/static/themes/ayu.css

@@ -518,7 +518,7 @@ kbd {
 }
 
 #theme-choices > button:hover, #theme-choices > button:focus {
-	background-color: rgba(70, 70, 70, 0.33);
+	background-color: rgba(110, 110, 110, 0.33);
 }
 
 @media (max-width: 700px) {