When we talk about background images, @import, and more, we use the url() function to load a resource:

div {
  background-image: url(test.png);
}

In this case I used a relative URL, which searches the file in the folder where the CSS file is defined.

I could go one level back

div {
  background-image: url(../test.png);
}

or go into a folder

div {
  background-image: url(subfolder/test.png);
}

Or I could load a file starting from the root of the domain where the CSS is hosted:

div {
  background-image: url(/test.png);
}

Or I could use an absolute URL to load an external resource:

div {
  background-image: url(https://mysite.com/test.png);
}

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