You can take care of this using CSS. Css contains functionality to 'size' objects in serveral ways, one of them is percentage :
#container { background: #0000FF; }
.fullWidth { width: 100%; }
and in your HTML file, you include the CSS file and write for example the following object :
<div id="container" class="fillWith">
Wow, this container uses 100% of my browser's available width!
</div>
See
this[
^] example for more information!
Have fun,
Eduard