How can I set a css border on one side only

Question

I want to only show a border on a specific div's left, right, top, or bottom side.

As of right now, I have the following, which creates a border on all sides:

#testdiv {
   border: 1px solid;
}

What do I need to do in order to have a border only on the left side?

Answer 1

Use four values to add a border to only one side of the element (write none to the side you want no border to appear). Use two values to add a border to the top and bottom sides (write none to the second value).