You may want to theme or override so much of Blaze that you should really build a customised version. The best approach is to grab the code from GitHub, change the variables and mixins and build the toolkit yourself.
Install node modules per folder:
cd scss && npm i gulp -g && npm i
To build Blaze run:
npm run build
The output of your changes will be available in /dist
If you want to build the solution every time you make a change
npm run watch will watch the appropriate files.