Huawei P20 Lite Case

Works well with both PLA and TPU (the ones I tested), without any support, but I had a heated bed at 85 for TPU.
I do use a brim on surfaces that need to be straight in the end, to avoid any possible edge warping.

A thing you can try: pause the print mid way of the bottom part of the cover and apply some brush strokes of your favourite colour paint (acrylic). It's going to look funky fresh.

Let your imagination go craaazy!