I am designing a UI for a developer portal based on spotify backstage. So far i have added google OAuth to the application. Now i want to change the login ui based on a predefined figma. I tried to read through the documentaion for backstage but I must confess I am new to typescript (in which backstage is written.) so the code is already pretty hard to understand for me and the documentation also doesn't really deal with the issue of how to create custom UI.

The closest i found was how to change the theme of the project like dark theme etc. I was wondering if there is a way to radically change the ui of the application.