To make sure no other elements CSS was inherited/affecting it I have created a test page with just the following CSS code.
<style>
#mainTop {
max-width: 300px;
border-bottom-right-radius: 1.5em;
border-top-right-radius: 1.5em;
border-top-left-radius: 1.5em;
border: 0.3em solid #FDBB30;
margin-bottom: .6em;
-webkit-box-shadow: 3px 6px 11px 0px #868686;
box-shadow: 3px 6px 11px 0px #868686;
padding: 0.3em;
}
</style>
…and HTML
<div id="mainTop">
<a class="twitter-timeline" data-dnt="true" href="https://twitter.com/LainesmeadSch" data-widget-id="664447718815883264" >Tweets by @LainesmeadSch</a>
<script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src=p+"://platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs");</script>
</div>
www.freeweelin.com/twittertest.html
Thanks