使class为row的盒子居中对齐该如何改进以上代码

要让class为row的盒子居中对齐，可以将float:left改为display:inline-block，并在父级元素上设置text-align:center。修改后的代码如下：

.row {
  padding: 50px 0 0 50px;
  display: inline-block;
  -moz-box-sizing: border-box;
  -webkit-box-sizing: border-box;
  -o-box-sizing: border-box;
  -ms-box-sizing: border-box;
  box-sizing: border-box;
  margin-left: -50px;
}

.row+.row {
  padding-top: 50px;
}

.row:after {
  content: '';
  display: block;
  clear: both;
  height: 0;
}

.row:first-child {
  padding-top: 0;
}

.row {
  padding-top: 0;
}

.row.flush {
  margin-left: 0;
}

.row.flush>* {
  padding: 0 !important;
}

.row.half {
  padding: 25px 0 0 25px;
}

.row.half+.row.half {
  padding-top: 25px;
}

.row.half {
  margin-left: -25px;
}

.row.double {
  padding: 100px 0 0 100px;
}

.row.double+.row.double>* {
  padding-top: 100px;
}

.row.double {
  margin-left: -100px;
}

.parent-element {
  text-align: center;
}

需要注意的是，父级元素的class为parent-element，这个class可以自己定义，根据实际情况修改。