You can hide an element in CSS by using either the “display” property or the “visibility” property.
The “display” property:
```
element {
display: none;
}
```
This will remove the element completely from the document flow, meaning it will not take up any space in the layout even though it’s still in the HTML.
The “visibility” property:
```
element {
visibility: hidden;
}
```
This will make the element invisible, but it will still take up space in the layout. The element is hidden, but it still affects the layout as if it was there.