[css] How to make this Header/Content/Footer layout using CSS?

Try this

CSS

.header{
    height:30px;
}
.Content{
    height: 100%; 
    overflow: auto;
    padding-top: 10px;
    padding-bottom: 40px;
}
.Footer{
    position: relative;
    margin-top: -30px; /* negative value of footer height */
    height: 30px;
    clear:both;
}

HTML

  <body>
    <div class="Header">Header</div>
    <div class="Content">Content</div>
    <div class="Footer">Footer</div>
  </body>