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

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).