content/static: remove highlighting from doc examples

Change-Id: Ifbc3675b3f6035fb90469daa1c66a239dc4ff346
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/288990
Trust: Jamal Carvalho <jamal@golang.org>
Run-TryBot: Jamal Carvalho <jamal@golang.org>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Julie Qiu <julie@golang.org>
diff --git a/content/static/css/unit_details.css b/content/static/css/unit_details.css
index 5ff2fe7..d80f175 100644
--- a/content/static/css/unit_details.css
+++ b/content/static/css/unit_details.css
@@ -48,7 +48,7 @@
   }
 }
 
-.UnitDetails :target:not(h2) {
+.UnitDetails :target:not(details, h2) {
   background-color: var(--yellow);
 }
 .UnitDetails-outline {