It can vary a bit. Riot is heavily programming/artist oriented so their dress code seems to be pretty lax. That being said if you have positions where you have to interact with other people in person/are important enough then you tend to dress a bit more nicely. For example casters at Riot games all wear suits and ties. Most of their workforce though? Pretty casual.
I know the two heads of Riot tend to dress pretty snappy since they are the heads and need to make an impression, but you can even find images of them working in clothing similar to what I linked.
Dress codes of course change depending on your role in a company. If you don't really need to interact with others then nice clothes aren't as important.