TL;DR: check out SenseTheme.
At Bitmetric, my colleagues and I regularly meet after work to investigate and experiment with interesting methods and technologies, share knowledge and generally shoot the breeze (we’re all at different client sites during the week, so it’s a good time to catch up).
The topic of our last meetup was Qlik Sense Themes. This is one of the big new (and highly anticipated) features in the Qlik Sense February 2018 release, allowing you to create custom themes for your apps. Our expectation was that we’d get the general idea of themes, go over the syntax and build a few cool themes. In reality, our meetup quickly devolved into a hunt for missing curly braces, property names and CSS classes. Still fun, if you’re into that sort of thing, but not as productive as we’d hoped.