size-units

reference) css units - w3cschools

Absolute sizes

px: pixel,

and others..

Relative sizes

Unit	Description
em	2em means 2 times the size of the current font
rem	Relative to font-size of the root element
vw	1% of the width of the viewport
vh	1% of the height of the viewport
vmin	1% of viewport's* smaller dimension
vmax	1% of viewport's* larger dimension
%	Relative to the parent element

and others...