I simply have the documentation open, which is really excellent and doesn't require any other sources. I begin with copying one basic example and building from

I simply have the documentation open, which is really excellent and doesn't require any other sources. I begin with copying one basic example and building from there. Then I'll tweak the HTML+CSS live in the browser's DevTools until I feel I understand what's happening in the CSS, I switch back to IntelliJ and bake my tweaks into my own custom SCSS extending bootstrap's classes and building on them. Never bought templates as I have the feeling that template authors don't really have the time to really grasp the concepts of bootstrap, nor do they care, and simply tend to pile tons of rules until they have some effect they desire. I felt it's always easier to simply read the docs, and occasionally jump into IRC in ##bootstrap or #css or their Slack when I'm stuck.