5/header.php

<!DOCTYPE html>
<!--[if lt IE 7]>      <html class="no-js lt-ie9 lt-ie8 lt-ie7"> <![endif]-->
<!--[if IE 7]>         <html class="no-js lt-ie9 lt-ie8"> <![endif]-->
<!--[if IE 8]>         <html class="no-js lt-ie9"> <![endif]-->
<!--[if gt IE 8]>      <html class="no-js"> <!--<![endif]-->
<html>
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <title>page</title>
        <meta name="description" content="">
        <meta name="viewport" content="width=device-width, initial-scale=1">
        <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/bootstrap@4.4.1/dist/css/bootstrap.min.css" integrity="sha384-Vkoo8x4CGsO3+Hhxv8T/Q5PaXtkKtu6ug5TOeNV6gBiFeWPGFN9MuhOf23Q9Ifjh" crossorigin="anonymous">

    </head>
    <body>

    <nav class="navbar navbar-expand-lg navbar-dark bg-primary">
  <a class="navbar-brand" href="index.php">Tutorial</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNav" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  <div class="collapse navbar-collapse " id="navbarNav">
    <ul class="navbar-nav ml-auto">
      <li class="nav-item">
      <a class="nav-link" href="students.php"> Manage Student</a>
      </li>
      <li class="nav-item">
      <a class="nav-link" href="subjects.php"> Manage Subject</a> 
      </li>
      <li class="nav-item">
      <a class="nav-link" href="index.php"> Search</a>
      </li>
    </ul>
  </div>
</nav>


<div class="container main" style="min-height:85vh">
<div class="shadow-sm p-4 mb-5 bg-white rounded" >