Theming

You may use Sass to create a custom theme, the easier way is just importing your own variables before @ecomplus/storefront-twbs/scss/styles:

@import "variables";
@import "node_modules/@ecomplus/storefront-twbs/scss/styles";

Take a look on Bootstrap 4 variables (opens new window) as reference.

If you're using plain CSS only, you can also overwrite CSS vars on :root and naturally overwrite default components styles (it generates unnecessary stylesheets, not so good approach).