基本代码：
<?php
session_start();
if ((!isset($_SESSION['valid']) == true)) {
unset($_SESSION['valid']);
header('location:index.php');
}
?>
<!DOCTYPE html>
<html lang="pt-br">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Noticias sobre Vacina - Digital</title>
<!-- Bootstrap-->
<link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/bootstrap/5.1.0/css/bootstrap.min.css" integrity="sha512-F7WyTLiiiPqvu2pGumDR15med0MDkUIo5VTVyyfECR5DZmCnDhti9q5VID02ItWjq6fvDfMaBaDl2J3WdL1uxA==" crossorigin="anonymous" referrerpolicy="no-referrer" /> <link rel="stylesheet" href="css/styles.css">
</head>
<body>
<div class="cover-container d-flex w-100 h-100 mx-auto flex-column">
<nav class="navbar navbar-expand-lg navbar-dark bg-dark">
<div class="container">
<a class="navbar-brand" href="#">Noticias sobre a vacina</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse">
<ul class="navbar-nav mr-auto">
<li class="nav-item …