@media screen and (max-width: 768px) {
  header .logo a img,
  div.conteudo-topo .logo img {
    display: none;
  }

  header .logo a,
  div.conteudo-topo .logo a {
    background-image: url("https://cdn.awsli.com.br/825/825438/arquivos/logos-atuzl.png");
    background-size: contain;
    background-repeat: no-repeat;
    background-position: center;
    display: inline-block;
    width: 150px;
    height: 45px;
  }
}