Make sense of rounded corners on buttons | by Shan Shen | UX Collective
Rounded corners on cards and buttons can be helpful to users for differentiating between items and recognizing what is clickable.
Rounded corners are easier on the eyes. When we align cards in a row, it’s easier to count the total number of cards when they have rounded corners.
<mark class="xl xm if">Fully rounded buttons are excellent in interfaces that have adequate space.</mark>
Aesthetic Usability Effect | Laws of UX
18 "laws of UX": principles of user experience and how people interact with sites and online content. Some of this is visual design and visual communication; some is interaction design. I'm not sure that the Pareto principle is really a UX law, since it applies in many other situations, but you can stretch the definition a bit.