Make the trailing-whitespace CSS rule more specific

Bug: Issue 10710
Change-Id: I49a8029bc4bf48bcbfc743e72d2dc799f9e8691b

polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html

diff --git a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
index 4ccdf96..61e8603 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff/gr-diff.html
@@ -184,7 +184,12 @@
         /* >> character */
         content: '\00BB';
       }
-      .trailing-whitespace {
+      /* Is defined after other background-colors, such that this
+         rule wins in case of same specificity. */
+      .trailing-whitespace,
+      .content .trailing-whitespace,
+      .trailing-whitespace .intraline,
+      .content .trailing-whitespace .intraline {
         border-radius: .4em;
         background-color: var(--diff-trailing-whitespace-indicator);
       }