float:left居中对齐

<div class="M1180">
<div class="services">
<div class="serv_cell L">
</div>
<div class="serv_cell L">
</div>
<div class="serv_cell L">
</div>
</div>
</div>

.M1180{width:1180px;margin:auto;clear:both}
.services{overflow:hidden;margin:0 -30px -30px 0;}
.serv_cell{width:371px;margin-right:30px}