How to organize a lot of related blocks for facet search programatically? I am experimenting with Solr search and the Facet API, and I've created a search page that now has about a dozen facet blocks on it.

Right now it just looks like Block 1, Block 2, Block 3, Block 4, etc.

I would like to group these into categories, such as Category A (Blocks 1-3), Category B (Blocks 4-9), and Category C (Blocks 10-12).  Ideally these categories would be collapsible.

I already have way too many modules on my site so I want to avoid adding a new module (such as Block Group) to do this.

In this case, is CSS the way to go, or is there some aspect of Drupal that can help with this?
I ended up doing this with Panels.  I took the facet blocks and grouped them using mini panels, and then I used Panels Style Collapsible to allow them to be expanded or contracted as necessary.