Qlik Sense is headed to a more flexible and customizable environment regarding the interface. With Qlik Sense 3 and above, we can manually change the default Theme or create a custom one and use it on our apps by just adding /theme/<themename> at the end of the url.
First of all, for those that do not know, once Qlik Sense desktop is running, we can access the hub from a regular browser like http://localhost:4848/hub/my/work. Now if we add our theme at the end of the url, every app that we open, will use that theme. So, if we go to http://localhost:4848/hub/my/work/theme/yianni, this will open the hub. Every app like the "helpdesk Management" that is opened, will use that theme.
I have created a simple theme and I only changed the background color of the sheet container and it looks like this
In Qlik Sense 3.1.2 and above, the theme templates have been moved to C:\Users\<username>\AppData\Local\Programs\Qlik\Sense\Client\themes\old. So we can place our files there.
Some of us, including myself, have used the Theme.palette in our extensions like