Here the Opportunities Logo keeps shifting up/down depending on the viewing window size. If I view from my laptop its fine, but when I view the page from monitor or ipad, the logo isnt placed properly. Below is current code-Any idea how to dynamically allign it?

<apex:form id="form">
        <apex:pageBlock title="*** Opportunities" id="pgblock" tabStyle="Opportunity">
            <img src="{!$Resource.OppLogo}" style="margin-top: -3.5%; margin-left: -0.5%;"/>