You can import the CSS file on the sass file, then compile only the main sass file if itβs feasible. found this which may help you: https://stackoverflow.com/questions/7111610/import-regular-css-file-in-scss-file#:~:text=It%20is%20now%20possible%20to,will%20import%20your%20file%20directly.
You can combine CSS files. here is an example I have used. maybe you can compile sass to CSS and later combine using this method?
please check the sample
//combine CSS
mix.styles([
'resources/css/open-iconic-bootstrap.min.css',
'resources/css/animate.css',
'resources/css/bootstrap-datepicker.css',
], 'public/css/essentials.css');
for the completeness of the answer same kind of approach can be used to js files as follows,
// combine required js files
mix.combine([
'resources/js/vendors/jquery-migrate.min.js',
'resources/js/vendors/jquery.easing.1.3.js',
'resources/js/vendors/bootstrap-datepicker.js',
'resources/js/vendors/scrollax.min.js'
], 'public/js/essentials.js');
use this approach on your webpack.mix.js