Add left indent for definition lists

Use padding to make the lists stand out from surrounding text.

Author: Tim Bannister

assets/scss/_custom.scss

@@ -721,3 +721,13 @@ figure {
     }
   }
 }
+
+// Indent definition lists
+dl {
+  padding-left: 1.5em;
+
+  // Add vertical space before definitions
+  > *:not(dt) + dt, dt:first-child {
+    margin-top: 1.5em;
+  }
+}