@media screen and (max-width:640px){


    #navi{
        display: none;
    }

    #footer{
        font-size: 10px;
    }

    .btn{
        font-size: 12px;
        width: 300px;
    }
    .btn_box{
        width: 100%;
    }
    .height_clear{
        height: auto;
    }

}