p {

  font-size: 200%; /* Text becomes 2x the previous size */

}

​

/*

  % (% of the initial size)

  vw (% of the viewport width)

  vh (% of the viewport height)

  vi (1% of the viewport size in the direction of the root element's inline axis)

  vb (1% of the viewport size in the direction of the root element's block axis)

  vmin (the smaller of vw or vh)

  vmax (the larger or vw or vh)

*/