How can I reduce the build time of project styles with vendor imports?

Question

Sass

In the prestashop theme, everything is tied to bootstrap
The main style file theme.scss imports bootstrap and something else
, and there are custom styles that are rigidly tied to bootstrap variables and therefore it is not possible to split the code into separate files.
Accordingly, each minor edit rebuilds all the styles and it takes about 5 seconds.
Which greatly complicates the work
. Is it possible to somehow split this economy? So that the whole economy is not rebuilt at once, but only custom styles?
Thanks!!!
I use webpack 4
in main.js and import theme.scss file