Answers for "how to align a div at the center"

div align center

.center {
  text-align: center;
}

// or

<div style="text-align:center">
</div>

center a div

<div id="outer">
  <div id="inner">Foo foo</div>
</div>
//css:, demo with border
<style>
#inner {
  display: table;
  margin: 0 auto;
  border: 1px solid black;
}

#outer {
  border: 1px solid red;
  width:100%
}
</style>