Bug 1814063 - Minor tweak to site data settings dialog styles. r=mconley,settings-reviewers

I can repro the issue with a larger size in the CSS (though I couldn't
find a screen size+resolution combo that caused this "naturally").

That said, 36em seems quite a lot, so reduce it to 20em which is what
the other dialogs use.

Also, use max-height rather than height so that the box is smaller for
smaller lists. We know this list has at least two elements so it should
look fine.

Differential Revision: https://phabricator.services.mozilla.com/D168400

browser/themes/shared/preferences/siteDataSettings.css

@@ -43,7 +43,7 @@
 }
 
 #SiteDataRemoveSelectedDialog.multi-entry #removalList {
-  height: 36em;
+  max-height: 20em;
 }
 
 #SiteDataRemoveSelectedDialog > dialog {