Discussion board where members can learn more about Integration, Extensions and API’s for Qlik Sense.
Yes I can. Anyway it's important to realize this is pure HTML/CSS code and has very little to do with the underlying technology (Qlik Sense in this case). For sure you will find more answers, to those type of questions, on an HTML/CSS forum.
Coming back to your original question. To change the background just modify lines 109 to 113 in login.html file