css calc font size
/*Here a possible solution:*/
http://codepen.io/CrocoDillon/pen/fBJxu
p {
  margin: 0;
  font-size: calc(4vw + 4vh + 2vmin);
  /* See:
   * http://codepen.io/CrocoDillon/pen/jgmwt
   * For some math behind this
   */
}
/*Font-size is calculated with available size using a function that is not 
perfect, but may be adjusted to work well in some cases.*/
