@media(max-width:768px) {
    #header {
        margin-left:20%;
        font-size: 25px;
    }
    #img {
        margin-left:14%;
        margin-top:10%; 
    }
    body {
        width:640px;
        margin:0px;     
    }
    #ex {
        margin-left:10%;
        color:gray;
        font-size:17px;
    }
    #click {
        margin-left:45%;
        font-size:30px;
        color:blue;
    }
}
@media(min-width:1024px) {
    #header {
        margin-left:40%;
    }
    #img {
        margin-left:32%;
    }
    #ex {
        margin-left:32%;
        color:gray;
        font-size:17px;
    }
    #click {
        margin-left:47.5%;
        font-size:30px;
        color:blue;
    }
}