How to align column header to center in Visualforce page?

How to align column header to center in Visualforce page?

Sample Code:

Visualforce page:

<apex:page controller="Sample">
    <style type = "text/css">
        .colHeadr {text-align:center;}     
    </style>
<apex:form >
    <apex:pageBlock >
        <apex:pageBlockSection >
            <apex:pageBlockTable value="{!listEmp}" var="e">
                <apex:column value="{!e.Name}" headerClass="colHeadr"/>
                <apex:column value="{!e.Age__c}" headerClass="colHeadr"/>
            </apex:pageBlockTable>
        </apex:pageBlockSection>
    </apex:pageBlock>
</apex:form>
</apex:page>

Apex Class:

public class Sample {
    public List<Employee__c> listEmp {get;set;}
    public Sample() {
        listEmp = new List<Employee__c>();
        listEmp = [SELECT Name, Age__c FROM Employee__c];
    }
}

Output: