static: keep url <pre> at constant rendering height

static/index.html

@@ -50,14 +50,16 @@
         <div>
           <input id="tag" len="20" placeholder="tag"/>
         </div>
-        <pre id="tag-url"></pre>
+        <pre id="tag-url">
+        </pre>
       </article>
       <article>
         <h2>Follow posts by instance</h2>
         <div>
           <input id="instance" len="20" placeholder="example.xyz"/>
         </div>
-        <pre id="instance-url"></pre>
+        <pre id="instance-url">
+        </pre>
       </article>
     </section>
 

static/urlgen.js

@@ -7,7 +7,7 @@
                 var value = encodeURIComponent(inputEl.value.replace(/^#/, ""));
                 preEl.innerText = value ?
                     "https://" + document.location.host + "/" + id + "/" + value :
-                    "";
+                    "\n";
             }, 10);
         }
         inputEl.addEventListener('change', onChange);