Define css if javascript is not enabled

You could probably use HTML's noscript tag.

<noscript>
    <style type="text/css">
        .exampleclass img {height:250px}
    </style>
</noscript>

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EDIT: I'm going to actually side with Stephen's answer as being the best. While the above might work, it might not be valid/following best practices.

Stephen answered:

put a "no-js" class on your body element, and then remove it with JS at load, and use .no-js in the selector for your CSS

The class could also be placed on your html element and then all styling that should appear when JavaScript is not available can be prefixed with html.no-js before what the selector would be otherwise. This is what HTML5 Boiler Plate does, for example.

put a "no-js" class on your body element, and then remove it with JS at load, and use .no-js in the selector for your CSS