add mono font and rework codeblock css

src/lib/Heading.svelte

@@ -6,7 +6,6 @@
 </script>
 
 <style lang="scss">
-
     .h {
         position: relative;
     }
@@ -45,7 +44,7 @@
     }
 
     svg {
-        /* undo the reset that makes svg's block */
+        /* undo the reset that makes images block */
         display: inline;
         width: 1em;
         /* tiny tweak for optical alignment */

src/lib/Post.svelte

@@ -1,5 +1,6 @@
 <script context="module">
     import '$styles/prose.scss';
+    import '$styles/code.scss';
 
     import { onMount } from 'svelte';
     import { formatDate } from './datefmt.js';
@@ -23,21 +24,23 @@
 
 <style>
     .page {
+        /* 3-column grid: left gutter, center content, and right gutter */
         display: grid;
         grid-template-columns: minmax(0, 1fr) minmax(0, var(--content-width)) minmax(0, 1fr);
-
+        /* a bit of breathing room for narrow screens */
         padding: 0 0.5rem;
     }
 
+    /* container for the table of contents */
+    .left-gutter {
+        grid-column: 1 / 2;
+        justify-self: end;
+    }
+
     .title {
         grid-column: 2 / 3;
     }
 
-    .left-gutter {
-        grid-column: 1 / 2;
-        justify-self: end;
-    }
-
     .subtitle {
         font-size: 0.9em;
         font-style: italic;
@@ -100,7 +103,6 @@
     <meta property="og:url" content="https://blog.jfmonty2.com/{slug}">
     <meta property="og:description" content={description}>
     <meta property="og:site_name" content="Joe's Blog">
-    <link rel="stylesheet" href="/prism-dracula.css" />
 </svelte:head>
 
 <div class="page">