Add css class on selection box using in CHtml::dropDownList
CHtml::dropDownList(‘name’,‘Selected value’,‘value array’, array(‘default value 1’,‘other any value 2’));
check below example
echo CHtml::dropDownList(‘departure_dropoff_location-’ . $row[‘schedule_id’],$dropoffLocation,
$dropoff[$row['agency_id']],
array('empty' => '[Select Dropoff Location]','class' => 'departureschedulelocation','disabled'=>'desabled'));