docs(css): improve definition table style

Text in definition tables are now aligned to the top of the cell. These are used in
the API index page and makes it cleared what headings match what content.

Closes #5286

docs/src/templates/css/docs.css

@@ -543,6 +543,10 @@ pre ol li {
   margin-bottom:30px;
 }
 
+.definition-table td {
+  vertical-align: top;
+}
+
 .component-heading {
   text-transform:capitalize;
 }