How to put the Bootswatch theme locally?
The theme can not read the SCSS file. You have to covert them to CSS. To do this, follow the following instruction.

Create a new SCSS(Let's name it the &quot;custom.scss&quot;) and import all the SCSS to this file. and convert it to CSS.&quot;
In the new &quot;custom.scss&quot; file, import the &quot;_bootswatch.scss&quot; and &quot;_variables.scss&quot;. To do this, use the @import function. Add the following code to your &quot;custom.scss&quot;.
@import 'bootswatch', 'variables';

Use a SCSS compiler to covert the SCSS to CSS.
Covert the &quot;custom.scss&quot; file to &quot;custom.css&quot;, then minify the file to &quot;custom.min.css&quot;.

On your &quot;bootstrap_subtheme_front_office.libraries.yml&quot; file, include the &quot;custom.min.css&quot;. Add the following code below the &quot;css/style.min.css: {}&quot;
css/custom.min.css: {}