feat(core): Hide header in PWA

Signed-off-by: provokateurin <kate@provokateurin.de>

Author: provokateurin

core/css/header.css

@@ -269,3 +269,13 @@ header .emptycontent {
 		width: 48px;
 	}
 }
+
+@media (display-mode: standalone) or (display-mode: minimal-ui) {
+	#header {
+		display: none !important;
+	}
+
+	#content-vue {
+		margin-top: var(--body-container-margin);
+	}
+}