css - Prevent child div from overflowing parent div

Question

I have a parent div containing a header section and a body section. The parent div has a maximum height, but no minimum height.

See this example: https://jsfiddle.net/1o79a6nc/2/

#cont {
  padding: 5px;
  background-color: red;
  max-height: 150px;
  max-width: 50%;
}
#body {
  background-color: blue;
  overflow-y: auto;
  overflow-x: hidden;
}
#head {
  background-color: green;
}

<div id='cont'>
  <div id='head'>
    <div>Head</div>
  </div>
  <div id='body'>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
  </div>
</div>

Answer 1

You could simply set the container to flexbox.

#cont {
  padding: 5px;
  background-color: red;
  max-height: 150px;
  max-width: 50%;
  display: flex; /*added*/
  flex-direction: column; /*added*/
}

jsFiddle

#cont {
  padding: 5px;
  background-color: red;
  max-height: 150px;
  max-width: 50%;
  display: flex; /*added*/
  flex-direction: column; /*added*/
}
#body {
  background-color: blue;
  overflow-y: auto;
  overflow-x: hidden;
  flex: 1; /* added */
}
#head {
  background-color: green;
}

<div id='cont'>
  <div id='head'>
    <div>Head</div>
  </div>
  <div id='body'>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
    <div>Body</div>
  </div>
</div>