老师这个试半天就是不浮动

<div class="mid">

<div class="m-1">

<div class="m-1image">

<img src="images/b1.jpg">

</div>

<div class="m-font">

<h2 class="m-1fonth2">Confernce&nbsp;Hall</h2>

<h3 class="m-1fonth3">Lorem Ipsum is simply dummy text of the<br/>

  prnting and typesetting industry

</h3>

<p class="m-1fontp">Lorem Ipsum has been the industry's  standard  dummy<br/> 

text  ever  since  the  1500s,when anunknow printer <br/>

took a galley of type and scrambled it to make a type<br/>

specimen book

</p>

<h4 class="m-font4">EXEPLORE</h4>

</div>

</div>

<div class="m-2">

<div class="m-font">

<h2 class="m-1fonth2">Confernce&nbsp;Hall</h2>

<h3 class="m-1fonth3">Lorem Ipsum is simply dummy text of the<br/>

  prnting and typesetting industry

</h3>

<p class="m-1fontp">Lorem Ipsum has been the industry's  standard  dummy<br/> 

text  ever  since  the  1500s,when anunknow printer <br/>

took a galley of type and scrambled it to make a type<br/>

specimen book

</p>

<h4 class="m-font4">EXEPLORE</h4>

</div>

<div class="m-1image">

<img src="images/b2.jpg">

</div>

</div>

<div class="m-3">

<div class="m-1image">

<img src="images/b3.jpg">

</div>

<div class="m-font">

<h2 class="m-1fonth2">Confernce&nbsp;Hall</h2>

<h3 class="m-1fonth3">Lorem Ipsum is simply dummy text of the<br/>

  prnting and typesetting industry

</h3>

<p class="m-1fontp">Lorem Ipsum has been the industry's  standard  dummy<br/> 

text  ever  since  the  1500s,when anunknow printer <br/>

took a galley of type and scrambled it to make a type<br/>

specimen book

</p>

<h4 class="m-font4">EXEPLORE</h4>

</div>

</div>

<div class="m-4">

<div class="m-font">

<h2 class="m-1fonth2">Confernce&nbsp;Hall</h2>

<h3 class="m-1fonth3">Lorem Ipsum is simply dummy text of the<br/>

  prnting and typesetting industry

</h3>

<p class="m-1fontp">Lorem Ipsum has been the industry's  standard  dummy<br/> 

text  ever  since  the  1500s,when anunknow printer <br/>

took a galley of type and scrambled it to make a type<br/>

specimen book

</p>

<h4 class="m-font4">EXEPLORE</h4>

</div>

<div class="m-1image">

<img src="images/b4.jpg">

</div>

</div>

</div>

上面是HTML内容，

.mian .mid {

width:100%;

overflow: hidden;

margin-bottom: 0;

}

.mian .mid .m-1,.m-2,.m-3,.m-4{

width:25%;

min-height:700px;

}/*四个样式*/

.mian .mid  .m-font{

background: #07cbc9;

}

.mian .mid  .m-font4{

border: 1px black solid;

width: 102px;

height:45px;

background: black;

color:white;

text-align: center;

line-height: 45px;

margin-left:25%;

}

/*中间左侧内容*/

}

.mian .mid .m-1,.m-2,.m-3,.m-4{

float:left;

}/*中间浮动*/

这是css样式，怎么不浮动呢