Improvements

- Edit code colors and add a color for comments
- Add ::selection
- Small edits for cards: last-child and overflow
- Add card-sectioning (header, footer, pre)
- Change global hue for Primary color
- Remove border for pre
- Add querySelectorAll() for theme-switcher.js
- Update docs

scss/components/_card.scss

@@ -7,6 +7,7 @@ article {
   margin-right: -$spacing-gutter;
   margin-left: -$spacing-gutter;
   padding: $spacing-block $spacing-gutter;
+  overflow: hidden;
   background: var(--card-background);
   box-shadow: var(--card-shadow);
 
@@ -53,4 +54,9 @@ article {
       padding: $spacing-block*map-get($spacing-factor, "xl");
     }
   }
+
+  // Remove last-child margin bottom
+  > *:not(footer):not(pre):last-child {
+    margin-bottom: 0;
+  }
 }