Border around box?

In theory, you can style div.rotatingtweets in CSS. Something like:

div.rotatingtweets {
    border:2px solid black;
}

Awesome, that worked great.
I also added padding since the text is right up to the border but padding does not seem to work in this case, at least not for the border on the left and the top.

div.rotatingtweets {
border: 1px solid gray;
padding: 10px;
}
This is my site: https://dev.caprillicoaching.nl/wordpress/

Try adding the padding to the tweet itself.

div.rotatingtweet {
    padding-left: 10px;
    padding-right: 10px;
}