Why does inner DIV spill out of outer DIV?
<p>I have been long away from HTML and CSS, can't find the solution to this simple problem.</p>
<p>I have one div inside the other. Outer Black and inner orange.</p>
<p><a href="https://i.stack.imgur.com/hsZkE.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/hsZkE.gif" alt="enter image description here" /></a></p>
<p>My HTML and CSS is :</p>
<p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
<div class="snippet-code">
<pre class="snippet-code-css lang-css prettyprint-override"><code>#outer {
  position: fixed;
  width: 30%;
  height: 30%;
  background-color: black;
}
#inner {
  width: 100%;
  height: 100%;
  margin: 5px;
  background-color: orange;
}</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div id="outer"&gt;
  &lt;div id="inner"&gt;
  &lt;/div&gt;
&lt;/div&gt;</code></pre>
</div>
</div>
</p>
<p>Why is my inner DIV spilling out of the outer ? How do I fix it without giving fixed dimensions?</p>