assets
connection
    connection.php
controller
    Controller.php
include
    header.php
    footer.php
model
    Model.php
process
    add-data.php
view
    index.pp
    sales-form.php
    report.php
config.php
index.php

require_once("controller/Controller.php");
$controller = new Controller;
$controller->index();

public function index () {
    require_once('view/index.php');
}

<?php require_once("include/header.php"); ?>
    <a class="btn btn-primary" href="view/sales-form.php">Record a new sales</a>
    <a class="btn btn-success" href="view/report.php">Search Report</a>
<?php require_once("include/footer.php"); ?>

<?php require_once("../include/header.php"); ?>
<?php require_once("../include/footer.php"); ?>

<?php require_once('config.php'); ?>
html code....