Remove unwanted header padding on navbar wrapper pattern.

When <header> is used solely as a full-width colored wrapper around <nav>
(e.g. <header class="bg-primary"><nav class="container">), PicoCSS
body > header padding-block creates excessive height. Neutralize it
when <nav> is the only child.

Author: Amaury

css/mu.component.nav.css

@@ -54,6 +54,16 @@ nav a {
 :is(nav, :has(> nav)).bg-pop       { --nav-bg: var(--mu-pop); }
 :is(nav, :has(> nav)).bg-spark     { --nav-bg: var(--mu-spark); }
 
+/*
+ * Remove PicoCSS body > header padding when <header> is used solely as a
+ * full-width colored wrapper around <nav> (e.g. <header class="bg-primary"><nav class="container">).
+ * PicoCSS adds padding-block to body > header for structural headers with text content;
+ * when the only child is a <nav>, that padding creates unwanted extra height.
+ */
+body > header:has(> nav:only-child) {
+	padding-block: 0;
+}
+
 /* PicoCSS bugfix: nav dropdown full-width on Firefox (picocss/pico#701) — remove when fixed upstream */
 nav details.dropdown {
 	display: inline-block;