You can use style rules defined in the XDIME aggregator's Multi-Channel Server theme policy.
The XDIME aggregator's theme policy is specified on the wp_main canvas tag in the XDIME aggregator's JSPs. Portlets will inherit the XDIME aggregator's theme policy if they do not specify a theme policy on the portlet's canvas tag.
There are several style rules defined in the XDIME aggregator's theme policy. These style rules define several characteristics that may be used to affect the look and feel of a portlet's content. To use these style rules, include the style rule class name with the definition of the entity that should use the rule.
<canvas layoutname="/my_portlet_layout.mlyt" type="portlet" class="wpsPageBar">
<% remaining portlet markup goes here %>
</canvas>