.site-header-brand {
  display: block;
  flex: 0 1 340px;
  min-width: 0;
}

.site-header-logo {
  display: block;
  width: min(100%, 340px);
  height: auto;
  filter: invert(1);
}

@media (max-width: 640px) {
  .site-header-brand { flex-basis: min(340px, calc(100vw - 125px)); }
}