[css] make div's height expand with its content

You can use CSS Grid Layout. Support is rather wide at the moment: check it on caniuse.

Here is the example on jsfiddle. Also example with tons of text stuff.

HTML code:

<div class="container">
  <div class="header">
   Header
  </div>
  <div class="content">
   Content
  </div>
  <div class="footer">
   Footer
  </div>
</div>

CSS Code:

html, body {
  width: 100%;
  height: 100%;
  margin: 0;
}

.container {
  width: 100%;
  height: 100%;

  display: grid;
  grid-template-rows: 100px auto 150px;
  grid-template-columns: auto;
}
// style stuff