Were are the themed login and background art chooses i really want a jinx one.

ok so this is something i have seen on many you tubers videos is some amazing artwork made background for there ui of there favorite champion and i ask why can we not select a option to maby not to the same extent but to give us a bit of customization to our background even if its just like our login screen like i would to have a jinx themed background but i don't know were or hot to make that happen so if anyone knows please teel me thanks you . also p.s jinx is the best champion