经过逐个查找，是几个最常见的标签产生了冲突，删除即可。列出如下：

body {
  font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
  font-size: 14px;
  line-height: 1.42857143;
  color: #333;
  background-color: #fff;
}
* {
  -webkit-box-sizing: border-box;
     -moz-box-sizing: border-box;
          box-sizing: border-box;
}
*:before,
*:after {
  -webkit-box-sizing: border-box;
     -moz-box-sizing: border-box;
          box-sizing: border-box;
}

h1,
.h1,
h2,
.h2,
h3,
.h3 {
  margin-top: 20px;
  margin-bottom: 10px;
}