This scroll box has had a border added to it. You can add borders to anything in HTML - including scroll boxes.
HTML Code
<div dir="ltr" style="text-align: left;" trbidi="on">
<div style="border: 8px solid yellowgreen; height: 80px; overflow: auto; padding: 2%; width: 300px;">
TEXT HERE</div>
<div style="border: 8px solid yellowgreen; height: 80px; overflow: auto; padding: 2%; width: 300px;">
TEXT HERE</div>