This is very useful for HTML design understanding.
You can specify HTML tag unit in different ways.
Basically you used ‘%’ and ‘px’ in HTML.
See below list and you can get basic idea regarding HTML tag unit structure.
in – inch
cm – centimeter
mm – millimeter
em – 1em = current font size.
2em = 2 times the size of the current font.
pt – point (1 pt = 1/72 inch)
pc – pica (1 pc = 12 points)