#arbre{
margin-left:16%;
}

#cadre_I{
position:absolute;
left:739px;
float:left;
width:430px;
background-color: #eee;
}

#tableau5{
margin-left:45%;
}

#case1_ex17, #case2_ex17, #case3_ex17,#case4_ex17{
width: 3em;	
	
	
}