Bootstrap uses variables to control the styles applied by Bootstrap classes. Some of the variables that can be changed affect the colour scheme, breakpoints, font & sizing, which you can modify to style your application.
Verj.io Bootstrap Starter Apps contain a _bootstrapVariables.scss file which allows you to set all variable values in one place. The file can be found in the Modules>Shared>Client>SCSS folder. The Bootstrap variables file is imported to the style.scss file using:
@import “_bootstrapVariables”;