Set the height of the header in pixels

[elchininet]

Kiosk mode sets the height of the header in 0 changing the --header-height variable. This variable is used to set the height of the #view element in this way:

height: calc(100vh - var(--header-height) - env(safe-area-inset-top))

And 100vh - 0 fails because 0 doesn‘t have units. This is problematic with those themes that set a background in this specific element.

This pull request changes the value of the variable --header-height in 0px something that will fix this issue.

Closes #43

[elchininet]

Hi @NemesisRE,
Please, check this one. It is a small change to fix #43.
Regards