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CSS CSS Foundations Advanced Selectors Pseudo-Elements: ::before and ::after

Joseph Longo
Joseph Longo
1,074 Points

Help: the everything element!?!?

I asked this question in a previous post, but I think if I ask this question here, I will be able to receive more clarity on this topic.

*, *:before, *:after { -moz-box-sizing: border-box; -webkit-box-sizing: border-box; box-sizing: border-box; }

What does the above CSS mean/do, and when should I use it? I copied this code from the HTML forms wed design track. Basically, what does it do? Should I automatically just include this code in my CSS as good practice, EVEN IF I DO NOT understand it?

Thanks,

Joe

1 Answer

The * is known as the universal selector. Basically, it selects every element in your page. In this case, that box-sizing property is being applied to every element, as well as any :before or :after psuedo-elements, on the page.

This technique of setting the box-sizing property on every element to border-box is popular because it tells every element to include padding and borders in their defined width instead adding them to the width. This makes calculations a lot easier to handle since you can add padding and borders to an element without the width suddenly changing on you.

For further reading and even a more modern update on this technique, check out this great blog post by Paul Irish.