Fix layout of maplibre controls by only using pico in explicit parts …

…of the layout.

picocss is conflicting with maplibre - most notably the maplibre
controls have a silly amount of padding, so the controls look wonky.

Instead of applying picocss everywhere, we now "allow list" subtrees of
the DOM with the "pico" class.

It's kind of annoying, but it kind of seems like it has to be this way -
if we're going to have two strong design systems (pico and maplibre),
they need to be confined to their own respective domains.

web/src/App.svelte

@@ -2,7 +2,7 @@
   import onewayArrowUrl from "../assets/arrow.png?url";
   import logo from "../assets/logo.svg?url";
   import About from "./About.svelte";
-  import "@picocss/pico/css/pico.jade.min.css";
+  import "@picocss/pico/css/pico.conditional.jade.min.css";
   import initLtn from "backend";
   import type { Map } from "maplibre-gl";
   import { init as initRouteSnapper } from "route-snapper-ts";
@@ -89,16 +89,18 @@
   }
 </script>
 
-<About />
+<div class="pico">
+    <About class="pico" />
+</div>
 <Layout>
-  <div slot="top" style="display: flex">
+  <div slot="top" class="pico" style="display: flex">
     <button class="outline" on:click={() => ($showAbout = true)}>
       <img src={logo} style="height: 6vh;" alt="A/B Street logo" />
     </button>
     <Settings />
     <span bind:this={topDiv} style="width: 100%" />
   </div>
-  <div slot="left">
+  <div class="pico" slot="left">
     <div bind:this={sidebarDiv} />
 
     <hr />