function rn(from, to) {
  return ~~(Math.random() * (to - from + 1)) + from;
}

function rs() {
  return arguments[rn(1, arguments.length) - 1];
} 

function boxShadows(max) {
  let ret = [];
  for (let i = 0; i < max; ++i) {
    ret.push(`
      ${ rn(1, 100) }vw ${ rn(1, 100) }vh ${ rn(20, 40) }vmin ${ rn(1, 20) }vmin
      ${ rs('#F52D75', '#CCBD4F', '#32497F', '#EB4377') }
    `)
  }
  return ret.join(',');
}

const cloud = document.querySelector('#cloud');
function update() {
  cloud.style.boxShadow = boxShadows(120); 
}

window.addEventListener('load', update); 
document.addEventListener('click', update);