<form action="concursos.php" method="post">
    <button type="submit" class="button">Concursos</button>
</form>
<form action="eventos.php" method="post">
    <button type="submit" class="button">Eventos</button>
</form>
<form action="eleicoes.php" method="post">
    <button type="submit" class="button">Eleições</button>
</form>