Customize Pages Bar - dan7davis/Lambda GitHub Wiki
Append a new page to the existing Page list
$(".course-tabs").append'<li><a>New Page</a></li')
OR
Replace <a>New Page</a>
with your desired HTML---in this case a search box:
$(".course-tabs")
.append('<li><input type="text" class="form-control" name="query" placeholder="Enter your search query" value="" autocomplete="off" data-reactid=".0.0.1.0.0.0.0.0.0"></li>')