Gist for my article: WordPress: Add custom logo support to your theme. https://vanaf1979.nl/wordpress-add-custom-logo-support-to-your-theme/

custom-log.css

header {
  height: 70px;
  margin: 0px 0px 50px 0px;
}

header .logo {
  height: 100%;
}

.custom-logo-link {
  display: inline-block;
  height: 100%;
}

.custom-logo-link .custom-logo {
  display: block;
  max-height: 100%;
  width: auto;
}