em measure html 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: what is em in css

'em' units for the font-size property will be relative to the'font-size of the parent element'.
'em' units on other properties other than font-size will be relative to the
font-size of the current element. 'rem' units sizes will always be relative 
to the font-size of the root html element.