Well, if you make a responsive site sooner or later, imho, you may need to enter media queries.
So this is what I would do in your case. Something like adding:
@media (max-width: 900px) {
header {height: 70px;}
}
@media (max-width: 700px) {
header {height: 50px;}
}
@media (max-width: 400px) {
header {height: 30px;}
}
change the various steps to any window width in which your title will be smaller.
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