I had a list of boxes, and on hover I wanted to invert the colors.

div {
  background-color: #000;
  color: #fff;
}

So I added

div:hover {
  background-color:#fff;
  color:#000;
}

But then the box didn’t look like a box. So I added a border:

div:hover {
  background-color:#fff;
  color:#000;
  border: 4px solid #000;
}

but it looked weird because of course the border is added outside the box.

The best approach I found was to use the box-shadow property like this:

div:hover {
  background-color:#fff;
  color:#000;
  box-shadow: inset 0px 0px 0px 4px #000;
}

Here’s the result:

Lessons in this unit:

0:	Introduction
1:	How to center an element with CSS
2:	▶︎ CSS Border inside the element
3:	What are good CSS Breakpoint values for Responsive Design?
4:	How to debug CSS by bisecting
5:	How to disable text selection using CSS
6:	How to put an item at the bottom of its container using CSS
7:	CSS, how to select elements that do not have a class
8:	How to stick an element on the bottom of the page with flexbox
9:	How to apply padding to multiple lines in CSS
10:	Making a table responsive using CSS
11:	CSS url()
12:	How to make an element smaller or bigger with CSS
13:	Customizing visited links
14:	Fix extra space after inline element
15:	How to create a sidebar that’s sticky but also scrolls
16:	How to embed YouTube videos using the correct aspect ratio
17:	Responsive pre tags in CSS
18:	Responsive YouTube Video Embeds
19:	How to remove all CSS from a page at once
20:	How I added Dark Mode to my website
21:	How to add a simple dark mode