.nav > a img {
  width: 155px;
  height: auto;
  max-height: none;
}

.foot img {
  width: 155px;
  height: auto;
  max-height: none;
  filter: brightness(0) invert(1);
}

@media (max-width: 620px) {
  .nav > a img {
    width: 155px;
    height: auto;
  }
}