Add chapter headers

assets/css/app.css

@@ -3,17 +3,31 @@
                          "Times New Roman", serif;
 }
 
+/* Both of these are links to their own id. They keep the text colour they
+   had as plain numbers, since an underlined blue verse number in the middle
+   of a sentence reads as part of the text. */
+.v,
+.chapter-number a {
+  color: var(--bs-secondary-color);
+  text-decoration: none;
+}
+
+.v:hover,
+.chapter-number a:hover {
+  color: var(--bs-emphasis-color);
+}
+
 .v {
   font-size: .7em;
   font-weight: 700;
   vertical-align: super;
   line-height: 0;
   margin-right: .15em;
-  color: var(--bs-secondary-color);
   user-select: none;
 }
 
-.v:focus-visible {
+.v:focus-visible,
+.chapter-number a:focus-visible {
   outline: 2px solid var(--bs-primary);
   outline-offset: 2px;
   border-radius: 2px;