Use Firebug or Chrome Dev Tools to examine the HTML and CSS of your CF7 form in detail. Once you understand how the HTML and CSS is configured in your CF7 form, you should be able to see the CSS changes you need to change the appearance of the form to suit your requirements.
See Styling Contact Form for a general explanation of styling CF7 forms using CSS. If you are not familiar with CSS, this page also includes some links to where you can learn CSS.