As part of the upcoming Chrome 62, macOS <button> elements will have a border-radius property.

https://www.chromestatus.com/features/5743649186906112

The summary of changes:

Before these CLs, the default style for buttons was:

background-color: ButtonFace; /* (-> #C0C0C0) */
border: 2px outset ButtonFace;
padding: 2px 6px 3px 6px;

After these CLs, it is:

background-color: ButtonFace; /* (-> #FFFFFF) */
border-color: #D8D8D8 #D1D1D1 #BABABA;
border-radius: 4px;
border-style: solid;
border-width: 1px;
padding: 1px 7px 2px 7px;

https://bugs.chromium.org/p/chromium/issues/detail?id=546679#c13

Among other things, this will affect button.dropdown-item elements:

https://getbootstrap.com/docs/4.0/components/dropdowns/#menu-items

(background-color changed for emphasis)