It's got alpha transparency, you can only use PNG or GIF for that, the issue is that most sofware only saves proper transparency for 24-bit PNG while for 8-bit

It's got alpha transparency, you can only use PNG or GIF for that, the issue is that most sofware only saves proper transparency for 24-bit PNG while for 8-bit it becomes jagged. PNG quant does this properly, see here: https://pngquant.org/ https://pngquant.org/