Bug 1608541 - Make min-height in "remove site data" dialog apply to the root element again. r=dao

XUL windows are sized constrained by the min-width/height properties on the root
element. If there are none we do XUL layout calculations that apparently don't
always produce the results we want.

The change to make <dialog> not a root element broke this in some cases.

Differential Revision: https://phabricator.services.mozilla.com/D61597

--HG--
extra : moz-landing-system : lando

browser/themes/shared/incontentprefs/siteDataSettings.css

@@ -28,9 +28,12 @@
 /**
  * Confirmation dialog of removing sites selected
  */
+:root[windowtype="Browser:SiteDataRemoveSelected"] {
+  min-height: 36em;
+}
+
 #SiteDataRemoveSelectedDialog {
   padding: 16px;
-  min-height: 36em;
 }
 
 #contentContainer {