Question: I have been long away from HTML and CSS, can't find the solution to this simple problem.

I have one div inside the other. Outer Black and inner orange.

[![enter image description here](https://i.stack.imgur.com/hsZkE.gif)](https://i.stack.imgur.com/hsZkE.gif)

My HTML and CSS is :

```css
#outer {
  position: fixed;
  width: 30%;
  height: 30%;
  background-color: black;
}
#inner {
  width: 100%;
  height: 100%;
  margin: 5px;
  background-color: orange;
}
```

```html
<div id="outer">
  <div id="inner">
  </div>
</div>
```

Why is my inner DIV spilling out of the outer ? How do I fix it without giving fixed dimensions?

Answer: 
The answers above assume that you do not want the margin. If you, in fact, want the margins, then you can add `overflow: hidden;` to the #outer.
This is likely happening because your inner div is being pushed out of its parent by the margin. Have you tried setting 'inner' to position: absolute with left: 0 and top: 0 property?