Make scroll bars wider (#7060)

* Set scrollbars to 12 px wide rather than 8px

Should overwrite the setting in reset.scss. This is untested at this point.

* removes scrollbar height and width specifications from reset.scss and basics.scss

app/javascript/styles/mastodon/reset.scss

@@ -53,11 +53,6 @@ table {
   border-spacing: 0;
 }
 
-::-webkit-scrollbar {
-  width: 8px;
-  height: 8px;
-}
-
 ::-webkit-scrollbar-thumb {
   background: lighten($ui-base-color, 4%);
   border: 0px none $base-border-color;