var cur=Math.round(9*Math.random())
if (cur<=1)
document.getElementById('testata').className='sfondopre01' ;
else if (cur<=2)
document.getElementById('testata').className='sfondopre02' ;
else if (cur<=3)
document.getElementById('testata').className='sfondopre03';
else if (cur<=4)
document.getElementById('testata').className='sfondopre04';
else if (cur<=5)
document.getElementById('testata').className='sfondopre05';
else if (cur<=6)
document.getElementById('testata').className='sfondopre06';
else if (cur<=7)
document.getElementById('testata').className='sfondopre07';
else if (cur<=8)
document.getElementById('testata').className='sfondopre08';
else if (cur<=9)
document.getElementById('testata').className='sfondopre09';