<apex:page standardController="Opportunity" lightningStylesheets="true">
    <apex:detail subject="{!Opportunity.Id}" relatedList="true" title="true" rendered="{!Opportunity.Amount < 10}" />
    <apex:pageBlock rendered="{!Opportunity.Amount > 10}">
        <apex:pageBlockSection columns="1">
            <apex:pageMessage summary="Amount is less than 10" severity="warning" strength="3" />
        </apex:pageBlockSection>
    </apex:pageBlock>
</apex:page>