This is a way to selectively use features from bootstrap, for instance to add some more classes to an app that uses Angular Material

selective-bootstrap.scss

// ******************************************************************* //
// *** Make sure you install the package 'bootstrap-scss' from npm *** //
// ******************************************************************* //

// ******************************************************* //
// *** Functions and variables need to be loaded first *** //
// ******************************************************* //

@import "~bootstrap-scss/functions";
@import "~bootstrap-scss/variables";

// ************************************************************** //
// *** Enable the next line if you want to include all mixins *** //
// ************************************************************** //

//@import "~bootstrap-scss/mixins";

// ******************************************************************* //
// *** Or selectively enable mixins based on the features you need *** //
// ******************************************************************* //

//@import "~bootstrap-scss/mixins/alert";
//@import "~bootstrap-scss/mixins/background-variant";
//@import "~bootstrap-scss/mixins/badge";
//@import "~bootstrap-scss/mixins/border-radius";
//@import "~bootstrap-scss/mixins/box-shadow";
@import "~bootstrap-scss/mixins/breakpoints";
//@import "~bootstrap-scss/mixins/buttons";
//@import "~bootstrap-scss/mixins/caret";
//@import "~bootstrap-scss/mixins/clearfix";
//@import "~bootstrap-scss/mixins/float";
//@import "~bootstrap-scss/mixins/forms";
//@import "~bootstrap-scss/mixins/gradients";
@import "~bootstrap-scss/mixins/grid";
@import "~bootstrap-scss/mixins/grid-framework";
//@import "~bootstrap-scss/mixins/hover";
//@import "~bootstrap-scss/mixins/image";
//@import "~bootstrap-scss/mixins/list-group";
//@import "~bootstrap-scss/mixins/lists";
//@import "~bootstrap-scss/mixins/nav-divider";
//@import "~bootstrap-scss/mixins/navbar-align";
//@import "~bootstrap-scss/mixins/pagination";
//@import "~bootstrap-scss/mixins/reset-text";
//@import "~bootstrap-scss/mixins/resize";
//@import "~bootstrap-scss/mixins/screen-reader";
//@import "~bootstrap-scss/mixins/size";
//@import "~bootstrap-scss/mixins/table-row";
//@import "~bootstrap-scss/mixins/text-emphasis";
//@import "~bootstrap-scss/mixins/text-hide";
//@import "~bootstrap-scss/mixins/text-truncate";
//@import "~bootstrap-scss/mixins/transition";
//@import "~bootstrap-scss/mixins/visibility";


// ***************************************************************** //
// *** Enable the next line if you want to include all utilities *** //
// ***************************************************************** //

//@import "~bootstrap-scss/utilities";

// ********************************************************************** //
// *** Or selectively enable utilities based on the features you need *** //
// ********************************************************************** //

//@import "~bootstrap-scss/utilities/align";
//@import "~bootstrap-scss/utilities/background";
//@import "~bootstrap-scss/utilities/borders";
//@import "~bootstrap-scss/utilities/clearfix";
//@import "~bootstrap-scss/utilities/display";
//@import "~bootstrap-scss/utilities/embed";
//@import "~bootstrap-scss/utilities/flex";
//@import "~bootstrap-scss/utilities/float";
//@import "~bootstrap-scss/utilities/overflow";
//@import "~bootstrap-scss/utilities/position";
//@import "~bootstrap-scss/utilities/screenreaders";
//@import "~bootstrap-scss/utilities/shadows";
//@import "~bootstrap-scss/utilities/sizing";
//@import "~bootstrap-scss/utilities/spacing";
//@import "~bootstrap-scss/utilities/text";
//@import "~bootstrap-scss/utilities/visibility";

// *************************************************************************************** //
// *** Here you can enable the actual Bootstrap features                               *** //
// *** These features might depend on mixins and utilities that need to be enabled too *** //
// *************************************************************************************** //

//@import "~bootstrap-scss/alert";
//@import "~bootstrap-scss/badge";
//@import "~bootstrap-scss/bootstrap";
//@import "~bootstrap-scss/bootstrap-grid";
//@import "~bootstrap-scss/bootstrap-reboot";
//@import "~bootstrap-scss/breadcrumb";
//@import "~bootstrap-scss/button-group";
//@import "~bootstrap-scss/buttons";
//@import "~bootstrap-scss/card";
//@import "~bootstrap-scss/carousel";
//@import "~bootstrap-scss/close";
//@import "~bootstrap-scss/code";
//@import "~bootstrap-scss/custom-forms";
//@import "~bootstrap-scss/dropdown";
//@import "~bootstrap-scss/forms";
@import "~bootstrap-scss/grid";
//@import "~bootstrap-scss/images";
//@import "~bootstrap-scss/input-group";
//@import "~bootstrap-scss/jumbotron";
//@import "~bootstrap-scss/list-group";
//@import "~bootstrap-scss/media";
//@import "~bootstrap-scss/modal";
//@import "~bootstrap-scss/nav";
//@import "~bootstrap-scss/navbar";
//@import "~bootstrap-scss/pagination";
//@import "~bootstrap-scss/popover";
//@import "~bootstrap-scss/print";
//@import "~bootstrap-scss/progress";
//@import "~bootstrap-scss/reboot";
//@import "~bootstrap-scss/root";
//@import "~bootstrap-scss/spinners";
//@import "~bootstrap-scss/tables";
//@import "~bootstrap-scss/toasts";
//@import "~bootstrap-scss/tooltip";
//@import "~bootstrap-scss/transitions";
//@import "~bootstrap-scss/type";