docs: use all.css for prefixed styles (#1221)

* docs: remove .bx--content override

* docs(ui-shell): add note on UI Shell theming

* docs(grid): touch up grid examples

* docs(theme): wrap localStorage in try catch

So that the site still works in Safari with all cookies blocked.

* docs: use prefixed all.css

Without vendor prefixes, some styles are lost in Safari.

* docs: remove svelte-preprocess from svelte.config.js

examples/sapper/src/routes/_error.svelte

@@ -1,8 +1,6 @@
 <script>
   export let status;
   export let error;
-
-  const dev = process.env.NODE_ENV === "development";
 </script>
 
 <svelte:head>
@@ -12,7 +10,3 @@
 <h1>{status}</h1>
 
 <p>{error.message}</p>
-
-{#if dev && error.stack}
-  <pre>{error.stack}</pre>
-{/if}