Regarding - All supported themes updated to Joomla 3.4

I read an older blog post - All supported themes updated to Joomla 3.4 https://www.gavick.com/blog/templates-u ... joomla-3-4

Does this mean the css is updated for modern browsers?

I wanted to use the Game template for a large Web design but the gkMenu childcontent css wasn't working properly when I tried to use it prior to the Joomla 3.4 update.

Also, thanks for all the greatness Gavick designs.

Hi,
update in most cases means - fix issues , make compatible with new Joomla 3.4 / component, no new features.
Besides check change-logs: https://www.gavick.com/updates for each of them