simplify scss for disabled button

stylesheets/_global.scss

@@ -715,14 +715,11 @@ $loading-height: 16px;
     background: $color-loki-green-gradient;
     border-radius: 100px;
 
-    &[disabled='disabled'] {
+    &:disabled, &:disabled:hover {
-      &,
-      &:hover {
       background: $color-loki-dark-gray;
       cursor: default;
     }
   }
-  }
 
   #mnemonic-display {
     margin: 2em 8px;