feat: Add overlay to HippieClock

- Add method to create overlay element
- Use DateDisplay and TimeDisplay classes
- Add button to toggle display
- Update style for header
- Add methods to handle shapes

source/style/modules/_clock.scss

@@ -1,6 +1,12 @@
 @use "../hippie-style/hippie";
 
+@use "sass:map";
+
 .body_clock {
+	header {
+		z-index: map.get(hippie.$z-indexes, "content-top");
+	}
+
 	main {
 		display: flex;
 		flex-flow: column nowrap;