The header height is dynamically adjusted depending on the logo or banner you upload. If you\’re using a banner image it will stretch to the height of your banner. If you are using a logo, it will add padding around it
So for example on your page if you want to change the height of the banner, you can use this custom css (add this in page settings > other scripts > custom css)
.banner {
padding: 20px 0px;
}
Adjust the 20px value to adjust the padding