ConvertPageMessages.page

<apex:page controller="ConvertPageMessagesController" >
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
<apex:slds />
<style>
  .msgIcon {
    display: none!important
  }
  .customMessage * {
    color: #fff!important
  }
  .customMessage {
    margin: 5px 0!important;
    max-width: 1280px;
    opacity: 1!important;
    width: 100%;
    font-size: 12px;
    border: 0px;
    padding-left: 10px;
  }
  .message {
    opacity: .1
  }
</style>

<script>
  $(document).ready(function(){
    overridePageMessages();
  });

  function overridePageMessages(){
    var textureEffect = '';
    //Uncomment below line for texture effect on page messages
    //textureEffect = 'slds-theme--alert-texture';

    $('.warningM3').addClass('slds-notify slds-notify--toast slds-theme--warning customMessage '+textureEffect);
    $('.confirmM3').addClass('slds-notify slds-notify--alert slds-theme--success customMessage '+textureEffect);
    $('.errorM3').addClass('slds-notify slds-notify--alert slds-theme--error customMessage '+textureEffect);
    $('.infoM3').addClass('slds-notify slds-notify--toast customMessage '+textureEffect);

    $('.errorM3').removeClass('errorM3');
    $('.confirmM3').removeClass('confirmM3');
    $('.infoM3').removeClass('infoM3');
    $('.warningM3').removeClass('warningM3');
  }
</script>
<apex:pagemessages/>
</apex:page>

ConvertPageMessagesController.cls

/*
  Description: This class is creating dummy page messages.
*/
public class ConvertPageMessagesController{
    public ConvertPageMessagesController(){
        ApexPages.addmessage(new ApexPages.message(ApexPages.severity.FATAL,'Please enter Account name'));
        ApexPages.addmessage(new ApexPages.message(ApexPages.severity.ERROR,'Please enter Account number'));
        ApexPages.addmessage(new ApexPages.message(ApexPages.severity.WARNING,'Please enter Account phone'));
        ApexPages.addmessage(new ApexPages.message(ApexPages.severity.INFO,'Please enter Account site'));
        ApexPages.addmessage(new ApexPages.message(ApexPages.severity.CONFIRM,'Please enter Account industry'));
    }
}