There are many length units when writing CSS styles. Know the common and uncommon ones.
There are two types: absolute units and relative units.
Absolute units: will not change due to changes in the size of other elements.
px: Pixel, a point on a computer screen.
pt: point
pc: itchy
in: 寸 1in = 96px = 72pt = 6pc = 2.54cm
cm, mm, q are not commonly used
Relative units: will change relative to the size of an element.
rem: the size of the font relative to the html tag
em: the size of the font relative to the parent element
%: relative to the width of the parent element or the size of the font
vw: 1vw == 1% of the width of the viewport (viewable area of the browser)
vh: 1vh == 1% of the height of the viewport (viewable area of the browser)
vmin/vmax: The smaller/larger dimension of the 1% viewport width and height.
A brief summary.