I have tried this but it doesn't change it. I noticed that the initial value of 'Message user info block width' was 120px, but on the forums, when I inspect the element it shows the width is 140px:
.message-cell.message-cell--user {
flex: 0 0 140px;
}
I'd want to change it to 200px, but I can't find a way. Can anyone help?