rem w3school code example

Example 1: vh and vw

/*vh viewport height and vw viewport width*/
/*example*/
div
{
  display: inline-block;
  height: 100vh; /*THis will set height equal to the height of windows*/
  width: 100vw/*This will set width equal to width of windows*/
}

Example 2: css em

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

Example 3: em css

/*realative to the font-size*/