ids theme: tighten references scrollbox position and height

Reduce margin-top from 35px to 10px so the scrollbox sits closer to
the heading. Reduce max-height from 540px to 510px so the bottom of
the scrollbox stays above the IDS footer bar.

Change-Id: If7e488306f5a5b9a290679af76fad8cb74e8f7a9
diff --git a/inst/reveal.js-5.2.1/css/theme/source/ids.scss b/inst/reveal.js-5.2.1/css/theme/source/ids.scss
index 323eaf7..495ab63 100644
--- a/inst/reveal.js-5.2.1/css/theme/source/ids.scss
+++ b/inst/reveal.js-5.2.1/css/theme/source/ids.scss
@@ -611,8 +611,8 @@
   font-family: "Fira Sans Condensed", sans-serif;
   font-size: 16px;
   text-align: left;
-  margin-top: 35px;
-  max-height: 540px;
+  margin-top: 10px;
+  max-height: 510px;
   font-weight: 400;
   color: #253b43;
   overflow-y: auto;