Editing
Add your own CSS styles to /sass/theme/_child_theme.scss or import you own files into /sass/theme/understrap-child.scss
To overwrite Bootstrap or UnderStraps base variables just add your own value to: /sass/theme/_child_theme_variables.scss
For example: the “$brand-primary” variable is used by both, Bootstrap and UnderStrap. Add your own color like: $brand-primary: #ff6600; in /sass/theme/_child_theme_variables.scss to overwrite it. That will change automatically all elements who use this variable. It will be outputted into: /css/understrap-child.min.css and /css/understrap-child.css
So you have one clean CSS file at the end and just one request.