KickstartCassiopeia has the option to create rounded buttons on your website.
Doing this is very easy, and this article tells you where you can set this feature and what to set.
First: What it applies to: buttons and badges
Second: What it does: adds a 'border-radius' attirbute to the elements selected
Third: Where to set it? Go to your KickstartCassiopeia module, tab General, option Button border radius. You can set it between 0 and 2. Higher would not have any effect. For instance 0.5 or 1.2
The higher, the more rounded your buttons become!