Add find shortcut in browser.

src/style.css

@@ -366,6 +366,26 @@ button.playpen-header-button:hover,
   border-color: @pp_accent;
 }
 
+/* Find-in-page, in the same clothes as the nav bar above it: it is the same
+   kind of furniture, just one that comes and goes. */
+.playpen-find {
+  padding: 4px 6px;
+  background-color: @pp_surface;
+  border-bottom: 1px solid @pp_border;
+}
+
+/* A search with no results says so in the box's border rather than only in
+   the count beside it, which is easy to miss mid-typing. */
+.playpen-find-entry.error {
+  border-color: @pp_err;
+}
+
+.playpen-find-status {
+  margin: 0 4px;
+  font-size: 0.8em;
+  color: @pp_text_dim;
+}
+
 /* The pane currently filling its tab. The other panes are still open and still
    running, just not drawn, so this is marked quietly — a lit border rather than
    anything alarming. The header's toggle icon carries the rest of the message. */