CSS Default Units

Question

Can I change the default unit from pixel to mm? For example I want when move an element left and top to be in mm not in pixel?

Answer 1

Specifying CSS units is a requirement for non-zero values. Browsers may try to guess what you meant, but it would still be a broken stylesheet according to the standard.

I.e. there is no "default unit" in CSS2, it's just that the browser may try to help you out, although it may as well just ignore your statement that doesn't specify units as an invalid one.

Answer 2

No, that's not possible since different screens might have different sizes while still having the same resolution. Ultimately leading to pixel or relative notations.

Answer 3

No, you can not change the default unit, but it shouldn't be too much to just put the units there:

#foo {
    left: 22mm;
    top: 20mm;
}

You should always specify the unit nevertheless, because it is required and browsers might interpret unitless values differently.

Answer 4

AFAIK if no explicit unit was specified (like 'em' or '%') then "px" is concatenated to the value and there is no way to override this default behavior.

Answer 5

As there's no "default unit" and you need to provide the unit when positioning an element, you can just use "mm" instead of "px".

Answer 6

There is no 'default unit'. The CSS spec requires that a length (other than zero) that is missing a unit be treated as an error (and thus ignored).

In quirks mode (and you should almost never be using quirks mode, it makes life more difficult), most browsers will perform error recovery and assume you meant pixels (despite the spec forbidding this).

If you are working with screen media — avoid physical units. Most systems are not calibrated to calculate the DPI correctly (so when converting from physical units into something a monitor understands (pixels) they get it wrong).