How can I add a background image on my Search Form?

Hi,

Really simple, I am trying to add and image behind the “Search” form on my sidebar widget but do not know how.

This is the existing Search form code:

<form method="get" id="searchform" action="<?php bloginfo('home'); ?>">

<input type="text" class="searching" value="<?php the_search_query(); ?>" name="s" id="s" /><input class="submit" type="submit" value="<?php _e('Search Now', 'theme1955'); ?>" />

</form>

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The idea is for the search form to look more stylish and not just a simple bar.
Many thanks in advance.

Pablo