docs: add mobile support + seo

src/routes/getting-started/css.md

@@ -4,4 +4,8 @@ title: Writing CSS
 
 TODO
 
-Use `px` measurements. Use `hsl` for colors.
+Use `px` measurements. 
+
+Use `hsl` for colors.
+
+Use `margin-inline` (x) and `margin-block` (y). Use `inline` & `block` for `padding` too.