Question: Is it possible to create an operating system that loads a web browser without menu bars, tabs etc. and that is all it loads.

I do not mean like Chrome OS but I mean all it loads is a html page which can be interacted with like an ordinary web page e.g. google.com, youtube.com.

Also, if this is possible, I would prefer it to be a Linux based OS and Webkit based browser.

Answer: 
Use both classes and combine them like so:

```
.baseClass
{
    margin-top:3px;
    margin-left:auto;
    margin-right:auto;
    margin-bottom:0px;
}

.baseClass.otherClass /* this means the element has both baseClass and otherClass */
{
    background-image:url("images/worldsource/customBackground.gif");
    background-repeat:no-repeat;
    width:950px;
    height:572px;
}

```

The markup is as follows:

```
<div class="baseClass otherClass"></div>

```

Now, in this fashion you can override baseClass if necessary... and since you don't have to keep adding your new class names to the baseClass definition, it's a bit cleaner.
What you want to do is make some CSS apply to two different types of elements, but allow them to have some differences as well. You can do this using some simple HTML:

```
<div class="base">
    <div class"inherited">
    </div>
</div>

```

And CSS:

```
.base, .inherited{
    margin-top:3px;
    margin-left:auto;
    margin-right:auto;
    margin-bottom:0px;
}

.inherited{
    background-image:url("images/worldsource/customBackground.gif");
    background-repeat:no-repeat;
    width:950px;
    height:572px;
}

```

This will add the shared properties to both types of `div`, but specific ones only to derived `div`s