hover效果加边框不抖动

前两天遇到一个hover效果给整个div加边框的问题。

html 如下

 <div class="hot-recommend">
        <div class="wrapper">
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    </div>1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253

less文件

.offer-list{
        &:hover{            border:solid 2px #027CFF;
            height:372px;
            margin: -1px -2px 0-2px;
            .offer-list-item{                margin-top: -1px;
            }
        }        .underline{            border-bottom: solid 1px #e3e3e3;
        }        ul{            margin-left: 10px;
        }        .offer-list-item{            height: 372px;
        }
  }12345678910111213141516171819

遇到的主要问题是hover后文字抖动，并且边框不能完美覆盖之前每个div下部的分割线。 
解决方案： 
1 遮挡分割线，整个加hover的div上移1px。 
2 解决抖动问题，减少div的height。

方向是这两个，但是.first-list 的margin上移带来了其他问题，就是虽然高度设了，但hover时还是会向下掉1px。

这个问题找了好久，发现原来外层div margin为负时，并不会把这个div块都带着移动，里层的li就没有跟着移动，所以出现了怎么调都还是会看到div块向下抖动的问题，并且下边框还出现了遮住1px的问题。问题是ul层也没有设置overflow：hidden。

后来想到了给li用一个margin：-1px。两个问题一起解决啦。不过下边框被遮住的应该是是因为div设置的高度值问题。 
其实有种比较简单的解决方法，那就是hover之前给div加白色边框占位，hover改变border颜色。这样很简单，但是不够通用，在这里就用不了，因为页面上有一个div的左上角有一个背景图片，白色的边框会在上面留下痕迹。没办法用。

margin经常会出现无效的情况，之前有遇到过，在这里也总结一下。

1. margin-top失效

<div> 
<divclassdivclass="box1">float:left</div> 
<divclassdivclass="box2">clear:both;margin-top:20px;</div> 
</div> 1234

网上能找到的两种比较靠谱的解释：

1：“在CSS2.1中，水平的margin不会被折叠；垂直margin可能在一些盒模型中被折叠…”
2：当第一个层浮动，而第二个没浮动层的margin会被压缩，详见--浮动元素后非浮动元素的margin的处理。
得到解决问题思路：1一起浮动 2 两个div中间加一个div清除浮动。

2父元素里第一个子元素margin-top失效。它会默认为是父元素的margin。 
解决办法： 
1.给父容器box加overflow:hidden;属性 
2.父容器box加border除none以外的属性 
3.用父容器box的padding-top代替margin-top

参考文章：CSS中margin-top属性失效问题解决

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