CSS: left:0 or left:0px

Question

Does it matter if left is specified as left:0; or left:0px;? As far as I can tell it works either way without Firefox's error console complaining, but just wondering if they have the exact same meaning.

I'm writing some JavaScript that will be moving items and also making them expand / contract. I'm guessing that the answer to the above will also answer if height:0; is the same as height:0px;.

@ShivanRaptor Your comment is ambiguous. 0 has no unit for this problem in CSS. That's not an absolute fact. — Denys Séguret, Apr 02 '13 at 08:19
@dystroy OP is asking for CSS. So I think my comment is fine. — Raptor, Apr 02 '13 at 08:50

score 2 · Answer 1 · answered Apr 02 '13 at 07:35

Well, it's the same, but only in case of zero. Zero is zero, no matter what the unit.

If you specify dimension of the non-zero value, you have to specify a unit as well.

This is the left property spec:

'left'
Value:      <length> | <percentage> | auto | inherit

As you can see, it has a value of <length>.

Now, for the length (from the spec):

Lengths refer to distance measurements and are denoted by in the property definitions. A length is a dimension. A zero length may be represented instead as the ‘0’. (In other words, for zero lengths the unit identifier is optional.)

score 2 · Answer 2 · answered Apr 02 '13 at 07:36

2

If you put 0 inside some property in CSS. 0 hasn't unit. It's just zero and still be interpreted as 0 by browsers.

But if you put value > 0 you have to specify unit.

answered Apr 02 '13 at 07:36

Simon Dorociak

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score 1 · Accepted Answer · answered Apr 02 '13 at 07:34

1

For CSS, whatever the unit 0 is always 0. There is no reason to add this unit.

The spec makes it clear :

After a zero length, the unit identifier is optional.

answered Apr 02 '13 at 07:34

Denys Séguret

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Thanks, asking because in the JavaScript I would be writing `myElement.style.left = foo+"px";`. – asimes Apr 02 '13 at 07:35

score 0 · Answer 4 · answered Apr 02 '13 at 07:39

0

No it doesn't matter.

left:0px;
left:0%;

Is all equal to 0.

answered Apr 02 '13 at 07:39

Johan Sundén

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CSS: left:0 or left:0px

4 Answers4