image크기 반응형으로 만들기

<style type="text/css">
	.main_image {
        background-image: url("http://798beijing.com/wordpress/wp-content/uploads/2017/11/main.png");
        background-size: cover;
        background-repeat: no-repeat;
      	background-position: 50% 50%;
      	width: 100%;
    }
</style>
<div class="main_image"></div>

Reference