var background = {

start:function()
{
  var divID = document.getElementById('back');

  var text = '';

  for(var k = 0; k < 100; k++)
  { 
    var F = k / 100.;

    text += '<div style="position:absolute; left:0px; top:' + k + 'px; width:520px; height:1px;'+ this.getBColor1(F) + '"></div>'; 
  }

  for(var k = 99; k >= 0; k--)
  { 
    var F = k / 100.;

    text += '<div style="position:absolute; left:0px; top:' + (329 - k) + 'px; width:520px; height:1px;'+ this.getBColor2(F) + '"></div>'; 
  }

  divID.innerHTML = text;
},

getBColor1:function(F)

// calculates (1 - F) * rgb(255, 255, 255) + F * rgb(255, 240, 183)

{
  var G = Math.round( 255 - F * 15);
  var B = Math.round( 255 - F * 72);

  return 'background-color:rgb(255,' + G + ',' + B + ')';
},
  
getBColor2:function(F)

// calculates (1 - F) * rgb(255, 204,  0) + F * rgb(255, 240, 183)

{
  var G = Math.round( 204 + F * 36 );
  var B = Math.round(       F * 183);

  return 'background-color:rgb(255,' + G + ',' + B + ')';
}
}