At the top of the contact form add in:
<style>
input[type="reset"] {width: 30px;}
</style>
Obviously you can add any standard css in place of the width parameter.
-or-
You can add to your child theme’s style.css
input[type="reset"] {width: 30px;}
with this you might want to add in a class to your individual contact form(s) so you can style them differently, such as:
.brownform input[type="reset"] {width: 30px;}
Hope this helps.