Fix bug where link was not working when target page imported CSS (?!?)

- Links on index page were mysteriously not working
- Tracked problem to the fact that target page was importing CSS
- Solution: move CSS to global import (I think this is required as of 9.3 anyway)
- Ref: vercel/next.js#5598
- Note: may cause problems linking to sphinx files (?) which still import CSS,
             but appears to work fine in docs??? what??

Makes very little sense why this fixes it, and still a bit inconsistent. Luckily
the problem seems to be related only to the dev server + HMR (??)
Check how the built version works in CI...

Author: milesrichardson

design/Layout/BaseLayout/BaseLayout.js

@@ -1,6 +1,3 @@
-import "@csstools/normalize.css";
-import "../../css/base.css";
-
 import defaultTheme from "../../themes/defaultTheme";
 
 import { ThemeProvider } from "theme-ui";

docs/pages/_app.js

@@ -1,3 +1,6 @@
+import "@csstools/normalize.css";
+import "@splitgraph/design/css/base.css";
+
 import { DefaultSeo } from "next-seo";
 
 const SEO_BASE_URL = process.env.SEO_CANONICAL_BASE_URL;