The "important" boxes on the web pages all hang over to the right compared to all the other boxes. This is a result of the red highlight on the left side.
My proposed fixes is add a calculated width in a later element. I did this to fail more gracefully in browsers that don't support calc. Note the spaces in "90% - 11px" are required.
--- docbook.css.orig 2019-07-27 15:56:36.000000000 +1000
+++ docbook.css 2019-07-27 16:07:41.000000000 +1000
@@ -334,14 +334,18 @@
border: 1px solid #a00;
border-left: 12px solid #c00;
+ width: calc(90% - 11px);
Created attachment 206096 [details]
Proposed path for docbook.css