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.
Navigate to the directory in your command line and run:
npm i gulp -g
Make any changes you want to the code and run:
The output of your changes will be available in /dist
If you want to build the solution everytime you make a change
watch will watch the appropriate files.