In CSS, length is measured by either an absolute value or relative value. An absolute unit is a fixed value such as pixel, point, inches, etc while as a relative unit such as %, em etch is relative to the parent element.
Please keep in mind that, CSS unit is applicable only for a non-zero value. Specify length with value including its unit otherwise, it would not be work. If the length value is zero(0) then, in this case, you can remove the CSS unit.
CSS Absolute Unit
The absolute length units are fixed and measured by these units such as cm, mm, in, px, pt,pc.
|px *||pixels (1px = 1/96th of 1in)|
|in||inches (1in = 96px = 2.54cm)|
|pc||picas (1pc = 12 pt)|
|pt||points (1pt = 1/72 of 1in)|