Add style

This is just to see how it works on in Flask and Google App Engine,
later I'll do a proper layout.

static/css/style.css

@@ -0,0 +1,23 @@
+body {
+    font-family:
+        // Bootstrap v5.0 stack: https://getbootstrap.com/docs/5.0/content/reboot/
+		// Cross-platform generic font family (default user interface font)
+		system-ui,
+		// Safari for macOS and iOS (San Francisco)
+		-apple-system,
+		// Chrome < 56 for macOS (San Francisco)
+		BlinkMacSystemFont,
+		// Windows
+		"Segoe UI",
+		// Android
+		Roboto,
+		// Basic web fallback
+		"Helvetica Neue", Arial,
+		// Linux
+		"Noto Sans",
+		"Liberation Sans",
+		// Sans serif fallback
+		sans-serif,
+		// Emoji fonts
+		"Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol", "Noto Color Emoji" !default;
+}