How can I insert vertical blank space into an html document?

Read up some on css, it’s fun: http://www.w3.org/Style/Examples/007/units.en.html

<style>
  .bottom-three {
     margin-bottom: 3cm;
  }
</style>


<p class="bottom-three">
   This is the first question?
</p>
<p class="bottom-three">
   This is the second question?
</p>