A little side-project that the team at Bitmetric has built now that Custom Themes became available in the Qlik Sense February 2018 release: SenseTheme.
SenseTheme is a visual editor for Qlik Sense themes. You can start with a blank theme, customize an existing theme to your liking, or just download a ready-made theme from the gallery.
Give it a try and let me know what you think. Or share some cool themes that you've built