<apex:page standardController="Contact" extensions="RequiredStylingExt">
  <style>
    .requiredBlock {
       background-color:#CC0000;
       bottom:1px;
       left:-4px;
       position:absolute;
       top:1px;
       width:3px;
    }

    .requiredInput {
       height:100%;
       position:relative;
    }
  </style>
  
  <apex:sectionHeader title="Create Contact" />
  <apex:pageMessages />
  <apex:form >
    <apex:pageBlock mode="mainDetail">
      <apex:pageBlockButtons >
        <apex:commandButton value="Save" action="{!save}" />
        <apex:commandButton value="Cancel" action="{!cancel}" />
      </apex:pageBlockButtons>
      <apex:pageBlockSection title="Details">
        <apex:inputField value="{!contact.Salutation}"/>
        <apex:inputField value="{!contact.FirstName}"/>
        <apex:pageBlockSectionItem >
          <apex:outputLabel value="Last Name"/>
          <apex:outputPanel id="detailrequiredpanel" layout="block" styleClass="requiredInput">
            <apex:outputPanel layout="block" styleClass="requiredBlock" />
            <apex:inputText value="{!Contact.LastName}"/>
          </apex:outputPanel>
        </apex:pageBlockSectionItem>
        <apex:inputField value="{!contact.phone}" />
        <apex:inputField value="{!contact.email}" />
        <apex:inputField value="{!contact.fax}" />
      </apex:pageBlockSection>
    </apex:pageBlock>
  </apex:form>
</apex:page>

public with sharing class RequiredStylingExt 
{
    // the standard controller that is being extended
    private ApexPages.StandardController stdCtrl;
    
    // constructor
    public RequiredStylingExt(ApexPages.StandardController std)
    {
        stdCtrl=std;
    }
    
    // Validates that the contact name and one of email/phone is provided before 
    // delegating to the standard controller save method
    public PageReference save()
    {
        Contact cont=(Contact) stdCtrl.getRecord();
        Boolean error=false;
        
        if (String.IsBlank(cont.name))
        {
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, 'Please enter the contact name'));
            error=true;
        }
        
        if ( (String.IsBlank(cont.Email)) && (String.IsBlank(cont.Phone)) )
        {
            ApexPages.addMessage(new ApexPages.Message(ApexPages.Severity.ERROR, 'Please supply the email address or phone number'));
            error=true;
        }
        
        PageReference result=null;
        if (!error)
        {
            result=stdCtrl.save();
        }
        
        return result;
    }

}