/*

px - most popular
  + easy to use, understandable
  - static

mm, cm, pt, pc, in - has died, do not used anymore
  mm - millimeter
  cm - centimeter
  in - inches = 2.54cm
  pt - points = 1/72 inch
  pc - picas = 12pt

em - Relative to the font-size of the element (2em means 2 times the size of the current font)
rem - Relative to font-size of the root element

vw - 	Relative to 1% of the width of the viewport
vh - Relative to 1% of the height of the viewport
vmin - smallest from vw and vh
vmax  - biggest from vw and vh

<div style="font-size:24px"></div>
<style>
  html {
    font-size: 14px;
  }
  li {
    font-size: 0.8rem;
  }
</style>