function get_randomCssNum()
{
    var ranCssNum= Math.floor(Math.random()*16);
	//var ranCssNum= Math.floor(Math.random()*Number of CSS you Have);
    return ranCssNum;
}

function getaCss()
{
   var whichCss=get_randomCssNum();

    var cssName=new Array(16)
     // var cssName=new Array(Number of CSS you Have)
     cssName[0]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top0.css'>";
     cssName[1]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top1.css'>";
     cssName[2]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top2.css'>";  
     cssName[3]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top3.css'>";   
     cssName[4]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top4.css'>";  
     cssName[5]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top5.css'>";  
     cssName[6]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top6.css'>";   
     cssName[7]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top7.css'>";   
     cssName[8]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top8.css'>";  
     cssName[9]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top9.css'>";   
     cssName[10]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top10.css'>";   
     cssName[11]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top11.css'>";   
     cssName[12]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top12.css'>";   
     cssName[13]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top13.css'>";
     cssName[14]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top14.css'>"; 
     cssName[15]="<link rel='stylesheet' type='text/css' href='http://www.gruff.it/gruff/wp-content/themes/gruff/top15.css'>";        
     //17k is using 10 CSS files in this example.
     //for Add more CSS just add line like this 
     //cssName[Next Number]="<link rel='stylesheet' type='text/css' href='CSS FILE URL'>";
  	return cssName[whichCss]
  }
  document.write(getaCss());