Untitled

<!DOCTYPE html>
<html lang="pt-br">
    <head>
        <meta charset="utf-8">
        <meta http-equiv="X-UA-Compatible" content="IE=edge">
        <meta name="viewport" content="width=device-width, initial-scale=1">
 ...etc

header('Content-Type: text/html; charset=utf-8');

header('Content-Type: text/html; charset=ISO-8859-1');

$observacao = $_POST['observacao'];