.back_up{
    height: 70px;
    width: 70px;
    position: fixed;
    right: 20px;
    bottom: 20px;
    z-index: 60;
}

.btn_up{
	height: 70px;
	width: 70px;
    border-radius: 50%;
    border: 3px solid red;
	background: white;
	cursor: pointer;
	z-index: 100;
    display: none;
    transition: opacity 350ms;
    -webkit-transition: opacity 350ms;
    position: absolute;
    top: 3px;
    left: 3px;
}

.btn_up .btnCenter{
	display: flex;
	flex-direction: column;
	justify-content: center;
	align-items: center;
    height: 70%;
    margin: 15% 0;
}

.btn_up .btnCenter img{
	height: 100%;
}

@media (max-width: 550px){

    .back_up{
        right: 5px;
        bottom: 5px;
    }
    
    .btn_up{
        height: 40px;
        width: 40px;
        right: 15px;
        bottom: 15px;
        background: white;
        top: 2px;
        left: unset;
    }

}