Albert - 9 months ago 31

CSS Question

I want to know if this is possible using only CSS:

`Black White`

White Black

Black White

White Black

The name represents the colour background I want. In this jsfiddle, I've hardcoded it to show exactly what it is that I want, but the amount of divs will be dynamic, so I don't know how many there will be.

How do I achieve this?

Answer

You'll need to use the `:nth-child`

pseudo class here.

**OPTION 1**

This first option requires the use of 2 selectors

The first handles the styling of the divs in the left column of the grid. Numbering those ones gives us 1,5,9,13,... which you can express as `4n-3`

(4*1-3=1, 4*2-3=5, 4*3-3=9, 4*4-3=13, ...). This can also be expressed as `4n+1`

, if you prefer.

The second selector, to handle the styling of the divs in the right column, is more straightforward as that is simply every fourth `div`

, which can be expressed as `4n`

(4*1=4, 4*2=8, 4*3=12, 4*4=16, ...).

```
div{
background:#fff;
display:inline-block;
height:100px;
width:50%;
}
div:nth-child(4n-3),div:nth-child(4n){
background:#000;
}
```

`<div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div>`

**OPTION 2**

This second option achieves the same result with a single selector using the negation pseudo class `:not()`

.

The inverse selection to that in option one can be expressed using `4n-1`

and `4n-2`

(or `4n+3`

and `4n+2`

) so we'll select all the divs, excluding those that match these expressions.

```
div{
background:#fff;
display:inline-block;
height:100px;
width:50%;
}
div:not(:nth-child(4n-1)):not(:nth-child(4n-2)){
background:#000;
}
```

`<div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div><div></div>`

**FURHTER READING ON MDN**

- Overview of CSS pseudo classes
- More information on the
`:nth-child`

pseudo class - More information on the negation pseudo class

**ASIDE**

I tried my best to come up with a single expression to suit this but couldn't. If anyone has any success doing so, please let me know. The sequence we're looking to match is: 1,4,5,8,9,12,13,16,17,20,...