400px - pixels (device pixels)

20em - relative unit

20rem - root em

4.167in - inches

10.5833cm - centimeters

105.833mm - millimeters

300pt - points

25pc - picas

40ex - x-height

40ch - based on width of zero (0) character

50vw - viewport width

50vh - viewport height

50vmin - smaller of vw or vh

50vmax - larger of vw or vh