fix line height and add details

index.html

@@ -72,7 +72,16 @@ elements.</p>
 it’s just markup. This, for instance, is a regular paragraph.</p>
 <p>Look at this horizontal break:</p>
 <hr>
-<p>Lovely.</p>
+<p>Lovely. We can hide stuff in the <code>&lt;details</code>&gt;
+element:</p>
+<details>
+<summary>
+A short summary of the contents
+</summary>
+<p>
+Hidden gems.
+</p>
+</details>
 <h2 id="lists">Lists</h2>
 <p>This is a plain old bulleted list:</p>
 <ul class="incremental">