Criar a pasta
/var/www/html/app-mvc/src/view/_templates
E dentro dela o arquivo
header.php
Contendo:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8">
<title><?=APP_TITTLE?></title>
<meta name="description" content="">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<!-- JS -->
<!-- please note: The JavaScript files are loaded in the footer to speed up page construction -->
<!-- See more here: http://stackoverflow.com/q/2105327/1114320 -->
<!-- CSS -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css"
integrity="sha384-ggOyR0iXCbMQv3Xipma34MD+dH/1fQ784/j6cY/iJTQUOhcWr7x9JvoRxT2MZw1T" crossorigin="anonymous">
<link href="<?php echo URL; ?>css/custom.css" rel="stylesheet">
</head>
<body>
<!-- logo, check the CSS file for more info how the logo "image" is shown -->
<div align="center"><h1><?=APP_TITTLE?></h1></div>
<img class="center-img" src="<?php echo URL; ?>/public/images/mvc.png">
<div class="container">
<nav class="navbar-expand bg-dark navbar-dark">
<ul class="navbar-nav justify-content-center">
<li class="nav-item">
<a class="nav-link" href="<?php echo URL; ?>">Home</a>
</li>
<li class="nav-item">
<a class="nav-link" href="<?php echo URL; ?>customers">Customers</a>
</li>
</ul>
</nav>
</div>