I want to overwrite view button of the opportunity products so I can have specific fields based on the product type.

Here is the visual page code:
<apex:page standardController="OpportunityLineItem" extensions="overrideCon" sidebar="true" showHeader="true">
<apex:form >
<input value=" Save " class="btn" title="Save" name="save" type="submit"/>
<input value="Cancel" class="btn" title="Cancel" name="cancel" type="submit"/>
<apex:pageBlock id="xxxpb1">

Opportunity:&nbsp;&nbsp;{!opp.name}<br></br>
Product:&nbsp;&nbsp;{!pro.name}
Quantity: <apex:inputField value="{!OpportunityLineItem.Quantity}"/>
<apex:pageBlockSection id="xxxpbs2" rendered="{!OpportunityLineItem.Product2Id=='01t17000000BmMdAAK'}">
       product 1 fields
        </apex:pageBlockSection>
    
    <apex:pageBlockSection id="xxxpbs3" rendered="{!OpportunityLineItem.Product2Id=='01t17000000BmMTAA0'}">
        product 2 fields
    </apex:pageBlockSection>
    <apex:pageBlockSection id="xxxpbs4" rendered="{!OpportunityLineItem.Product2Id=='01t17000000BX9SAAW'}">
        product 3 fields
    </apex:pageBlockSection>   
</apex:pageBlock>
</apex:form>  
</apex:page>

Here is the apex code:

public class overrideCon {
private final ID oliId;
    public overrideCon (ApexPages.StandardController stdController) {
        this.oliId = (String)stdController.getId();
    }
    
    Opportunity opp;
    OpportunityLineItem oli;
    Product2 pro;

    public Product2 getPro(){
        if (pro == null) {
            pro = [select Id, name from Product2 where id = :getOli().Product2Id];
        }
    return pro;
    }
    public Opportunity getOpp(){
         if(opp == null){
              opp = [select Id, name, amount, Pricebook2.Name from Opportunity where id = :getOli().Opportunityid];
         }
         return opp;
     } 
     
     public OpportunityLineItem getOli() {
         if(oli == null){
             oli = [select Id, Product2Id, OpportunityID from OpportunityLineItem where ID = :oliID];
         }
         return oli;
     }   
     
     public PageReference save() {
        update oli;
        return null;
    }
    
    public PageReference cancel() {
    return null;
    }

   }


How do I get the save and cancel button to work so changes are saved.