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 framework yourself.
Step 1 Download
Go to Blaze's GitHub repo and either clone or download the source.
Step 2 Install
Navigate to the directory in your command line and run:
Step 3 Build
Make any changes you want to the code and run:
npm run build
Ready to go!
The output of your changes will be available in /dist