#cnblogs_post_body p {
font-family:"Comic Sans MS";
font-size:18px;
}

<div class="flex-center listing-img">
    <img v-if="item.imgUrl" v-bind:src="item.imgUrl" alt="not find picture">
    <img v-if="!item.imgUrl" src="../../assets/img/detail-not-image.png"alt="not find picture" v-sf-img>
</div>
 
.listing-img{
　　width: 100%;
   min-height: 270px;
   max-height: 320px;
}
.listing-img>img{
　　display: inline-block;
   height: auto;
   max-width: 100%;
   max-height: 320px;
}
.flex-center {
　　display: flex;
　　justify-content: center;
　　align-items: center;
}