CSS Units
px
An absolute measurement of pixels
%
Percentage relative to the size of the parent
em
Relative to font size of current element (if font size is 16px, 1em = 16px)
rem
Relative to font size of root element (usually <html>).
vw
1vw = 1% of viewport width
vh
1vh = 1% of viewport height
fr
A fractional measurement used by CSS grid. The value that an fr represents is determined by the sum of frs in a column/row.