Round simon buttons

Can someone help me get some round buttons on here? I have a table system, but if something better would work I’m open to anything. The buttons are rounded, but they don’t reach to the full size. Every time I try to get them larger they are no longer round! What is the best way to mark this up?

Use border-radius on each cell (you can use the existing color ids). e.g.:

#green { background-color: #8bc34a; border-top-left-radius: 100%; }

Repeat for each quadrant, changing the border radius directions (bottom-right, etc.) accordingly.