fix: change padding to margin in header

Otherwise there would be a much greater gap between header and main.
Header normally is styled by icluded style via head.php. This has the
correct margin. The padding-top from this local style.css did two gaps
together.

Signed-off-by: Conrad Zelck <git@simpel.cc>

style.css

@@ -65,7 +65,7 @@ a {
 }
 
 header {
-  padding-bottom: 1.5em;
+  margin-bottom: 1.5em;
 }
 
 nav {