Exacto como dijo Cluster puedes usar Fit on page.
Para que funcione con ProPortal creo que era así:
<script type="text/javascript" src="jscripts/fitonpage.js?ver=230"></script>
<script type="text/javascript">
<!--
var fitonpage_on = "{$mybb->settings['g33k_fitonpage_enabled']}";
var fitonpage_resize = "{$mybb->settings['g33k_fitonpage_resize']}";
var fitonpage_fluid = "{$mybb->settings['g33k_fitonpage_fluid']}";
var fitonpage_topbar_resized = "{$lang->fitonpage_topbar_resized}";
var fitonpage_topbar_full = "{$lang->fitonpage_topbar_full}";
var fitonpage_topbar_text_class = "{$mybb->settings['g33k_fitonpage_topbar_text_class']}";
var fitonpage_topbar_bground = "{$mybb->settings['g33k_fitonpage_topbar_bground']}";
var fitonpage_topbar_icon = "{$mybb->settings['g33k_fitonpage_topbar_icon']}";
var fitonpage_location = "portal";
-->
</script>