Reduce donate button size a bit

docs/css/extra.css

@@ -279,7 +279,7 @@ footer > hr {
   width: 35%;
   min-width: 240px;
   max-width: 280px;
-  height: 50px;
+  height: 40px;
   background-size: contain;
   background-repeat: no-repeat;
 }