<div id="st-integral-page">

    <div class="background-box">
        <img class="img-background" src="./img/ic_rebpack_background.png" alt="">
    </div>
</div>

/*把圖片做背景圖*/
 #st-integral-page .background-box {
     width: 100%;
     height: 100%;
     top:0;
     z-index: -1;
     position: absolute;
 }
/*把圖片做背景圖*/
 #st-integral-page .background-box .img-background {
     display: block;
     outline: none;
     border:0;
     height: 100%;
     width: 100%;
 }
 
 這樣圖片會變形.....