2
style.css,
find the 'xoopsCode' style and add a width value.
At xoops.org I think they use:
div.xoopsCode { font-size: 12px;
font-family: FixedSys, "Courier New",Courier,monospace;
background: #fffff8;
border: 1px solid #6C87B0;
color: #385a72;
width: 95%;
height: 200px;
margin: 0.5em;
overflow: auto;
padding: 3px 3px 3px 3px;
}
Tip - I found this by using the firefox Web Developer extension