So I did read that css doesn't work in forum posts. But it's plain to see everywhere that a lot of people have access to css customization (such as background-image:url("blahblah.png");padding:20px; and all that sort of thing) in their forum posts, and not a single html guide anywhere explains how people are getting this, only the basic stuff like <*b>bold text.

How do people then get css customization in their forums, like the gray backgrounds in this post: https://www.lioden.com/topic.php?id=69533570020

Here's essentially what I tried to code in my art post (minus the asterisks, and with 's at the end), and it worked perfectly in preview, but of course as you can see, nothing worked in practice. https://www.lioden.com/topic.php?id=304429371762

<*div style="background:url("https://orig14.deviantart.net/2dd6/f/2016/207/5/4/dabgs_by_priestessshizuka-dabgc9u.png"); background-size:100%; padding:50px;"><*div style="width:100%; background-color:rgba(0,0,0,0.5); border:1px solid #000000;color:#999999; padding:20px; text-align:justify; font-family:trebuchet ms; box-shadow:0px 0px 6px 2px #ffffff; text-shadow:0px 0px 3px #ffffff; font-size:12px; line-height:16px; text-transform:lowercase;">