In order to consistently style some form elements (checkboxes, radio, selects) you need to use javascript. There isn't a way to do specifically what you are looking for cross-browser / platform in ...
Does ars civis really need to force ORANGE selection? This makes highlighted text much harder to read (offending excerpt from Ars Civis css: * ::selection { color: #fff; background:#ff4e00 } MDN ...