Change checkbox shape?

[mitten]

I've looked through all the settings, and I'm sure I've just missed it somewhere, but I can't see where to change the shape of the checkboxes from round to square. Can someone point me at where to change the box shape? And if there isn't a setting, does anyone know which CSS selectors to use to change it? Thanks so much!

[Akifyss]

You can import the following CSS snippet to make it square:

body {
    --checkbox-radius: 4px;
}