Some people believe rounded corners are better recognoziable by humans. So here are your radius helper classes. There are three sizes, defined by space CSS vars, options for all directions as well as an extra pill-look class and a perfectly rounded square, AKA circle.
When no direction is given, the border radius will apply on all for corners. When a cardinal direction (t,r,b,l) is present, radius will apply on two corners. When a diagonal direction (tr,br,bl,l) is given, only one corner will be rounded.