The ch unit for CSS specifies the length of the element relative to the narrow glyph of the element.
The narrow glyph is represented by the “0” (ZERO, U+0030) glyph.
<number>ch
cap
em
ex
ic
rem
cm
cqb
cqh
cqi
cqmax
cqmin
cqw
deg
dpcm
dpi
dppx
dvb
dvh
dvi
dvmax
dvmin
dvw
grad
in
lvb
lvh
lvi
lvmax
lvmin
lvw
mm
ms
pc
pt
px
Q
rad
s
svb
svh
svi
svmax
svmin
svw
turn
vb
vh
vi
vmax
vmin
vw
World Wide Web Consortium (W3C)