// JavaScript Document
function image_random() {
  number = 30;
  var colonna = document.getElementById('container');
  colonna.style.cssText = "background-image: url(../img/random/pic_"+ Math.floor(Math.random() * number) +".jpg);";
};

function image_long() {
  var colonna = document.getElementById('container');
  colonna.style.cssText = "background-image: url(../img/laterale_big.jpg);";
};