Mybb default theme classic postbit author postbit border css help

[lkop]

i want to add a right side border with no radius corner. can someone please tell me what am I doing it wrong?
it is default MyBB theme.

https://i.postimg.cc/4x2c65jy/image.png

.post.classic .post_author {
	border-right: 1px solid #ddd;
	float: left;
	width: 15%;
	margin: 0 1% 15px 0;
	border-left: 0;
	padding: 5px 1%;
}

got it, it's in css3 file.