Single post in A Somewhat Extensive Guide to BBCodes

How do I get,for example an 80% wide hide box, to be aligned in the centre? e.g edit; Btw, I know I can just use the margin-left code with percentages, eg .panel {text-align: center; width: 60%; &>div { background: white; color: black; border:1px solid black; text-align:center; margin-left: 15%;}} but I'm kinda hoping there's an easier way >.<