Website Moblie First nên chọn cách nào để tối ưu tốc độ?

Cách 1:

#set1:before {
    position: absolute;
    background: url(../img/deco.png);
    content: '';
    background-size: 100%;
    right: -18%;
	top: -2vw;
	width: 86%;
	height: 110vw;
}
@media only screen and (min-width: 768px){
	#set1:before {
        right: auto;
		left: calc(50% - 87px);
		top: -34px;
		width: 795px;
		height: 876px;
	}
}

Cách 2:

#set1:before {
    position: absolute;
    background: url(../img/deco.png);
    content: '';
    background-size: 100%;
}
@media only screen and (max-width: 767px){
	#set1:before {
		right: -18%;
		top: -2vw;
		width: 86%;
		height: 110vw;
	}
}
@media only screen and (min-width: 768px){
	#set1:before {
		left: calc(50% - 87px);
		top: -34px;
		width: 795px;
		height: 876px;
	}
}