Apex variable to Display the value and change the css

Visualforce Page:

apex variable to Display the value and change the css .

<style>

.un_rvw{ color.green}
.incp {color.green}
</style>

<td style="text-align:left;">

<apex:outputPanel rendered="{!Case.Status != null}">

<apex:variable var="casePublicStatus" value="{!IF(Case.Status = 'Approved', 'Approved', IF(Case.Status = 'Rejected', 'Rejected', IF(Case.Status = 'Cancelled', 'Cancelled', IF(Case.Status = 'Application Complete', 'Completed', IF(Case.Status = 'Exit Confirmed', 'Exited', IF(Case.Status = 'Final Rejection' || Case.Status = 'Rejected' || Case.Status = 'Rejected by Immigration' || Case.Status = 'Rejected by Immigration 1' || Case.Status = 'Rejected by Immigration 2' || Case.Status =  'Rejected by Typing Dept' || Case.Status = 'Refund Issued', 'Rejected','In Process'))))))}"/>
<apex:variable var="casePStatus" value="{!Case.Public_Status_WF__c}"/>

<apex:variable var="caseCSS" value="{!IF(casePStatus= 'Approved', 'aprv',IF(casePStatus= 'Cancelled' || casePStatus= 'Rejected' || casePStatus= 'Warning', 'rjct', IF(casePStatus= 'Completed' || casePStatus= 'Exited', 'aprv',  IF(casePStatus= 'Pending Payment', 'pend',  IF(CONTAINS(casePStatus, 'Incomplete'), 'incp', 'un_rvw')))))}" />

<span class="sts {!caseCSS}" style="margin-left:-8px;">{!casePStatus}</span>

</apex:outputPanel>
</td>