1. div鼠标悬停控制子控件显示与隐藏

  悬停在父辈div上,子div显示

.son{
display: none;
}
 
.father:hover .son{
display: block;
}<br><br><div class="father"><br>    SHOW<br>  <div class="son"><br>    oky<br>  </div><br></div>


 2.相邻div控制控件显示与隐藏(下面的隐藏和显示)

.two{
      display: none;
    }

    .one:hover + .two{
      display: block;
    }    

<div class="one">
    oky
</div>
<div class="two">
    show
</div>