margin is a simple CSS property that has a shorthand syntax I keep forgetting about, so I wrote this reference post
margin CSS property is commonly used in CSS to add space around an element.
marginadds space outside an element border
paddingadds space inside an element border
Specific margin properties
margin has 4 related properties that alter the margin of a single edge at once:
The usage of those is very simple and cannot be confused, for example:
margin-left: 30px; margin-right: 3em;
margin is a shorthand to specify multiple margins at the same time, and depending on the number of values entered, it behaves differently.
Using a single value applies that to all the margins: top, right, bottom, left.
Using 2 values applies the first to bottom & top, and the second to left & right.
margin: 20px 10px;
Using 3 values applies the first to top, the second to left & right, the third to bottom.
margin: 20px 10px 30px;
Using 4 values applies the first to top, the second to right, the third to bottom, the fourth to left.
margin: 20px 10px 5px 0px;
So, the order is top-right-bottom-left.
margin accepts values expressed in any kind of length unit, the most common ones are px, em, rem, but many others exist.
It also accepts percentage values, and the special value
auto to center elements
auto can be used to tell the browser to select automatically a margin, and it’s most commonly used to center an element in this way:
margin: 0 auto;
As said above, using 2 values applies the first to bottom & top, and the second to left & right.
The modern way to center elements is to use Flexbox, and its
justify-content: center; directive.
Older browsers of course do not implement Flexbox, and if you need to support them
margin: 0 auto; is still a good choice.
Using a negative margin
margin is the only property related to sizing that can have a negative value. It’s extremely useful, too.
Setting a negative top margin makes an element move over elements before it, and given enough negative value it will move out of the page.
A negative bottom margin moves up the elements after it.
A negative right margin makes the content of the element expand beyond its allowed content size.
A negative left margin moves the element left over the elements that precede it, and given enough negative value it will move out of the page.