body{
    background:url(why_02.jpg) no-repeat;   background-size:100% auto;
    /*background:url(why_02.jpg) no-repeat center top;
    background-size:cover;*/
}

header{
    width: 1002px;
    margin: 0 auto;

}

/*头部*/

.logo_01{ width:31%; /*width:387px; */ height:154px; margin-top:43px; margin-left:24px; }
.logo_01 img{ width:100%; height:auto;}
/*/头部*/