https://access.redhat.com/knowledge/docs/en-US/JBoss_Data_Grid/6/html-single/API_Documentation/files/api/overview-summary.html Description of problem: It looks like if the choice is made to display the javadocs with frames it's completely missing and if the choice is made to display without frames the CSS doesn't work so well.
The bug listen in the dependency that tracks this issue for other API docs and this one is now resolved. Confirmed link in OP works, hence this bug is resolved.