我想要一个透明的div线分隔符。如何在CSS/html中做到这一点?

Basically I want a line like the ones that separate posts on stackoverflow, only I want it vertical and to be a kind of "left border" that will be in a separate div to display links and content. So instead of making a big rectangle on the left side with links and text, I just want like a really thin, subtle gray line that goes all the way down the page.Basically I want a line like the ones that sepa