Give rendered-data sections a background and some padding (#1195)

Gives definition sections for APIs, events, etc a background and a small indent, which I find very helpful to guide the eye.

layouts/partials/openapi/render-object-table.html

@@ -21,7 +21,7 @@
 
 {{ if $properties }}
 
-<table{{ if .anchor }} id="{{ .anchor }}"{{ end }}>
+<table{{ if .anchor }} id="{{ .anchor }}"{{ end }} class="object-table">
  {{ with $title }}
  <caption>{{ . }}</caption>
  {{ end }}