Set id for search input

Author: toshimaru

src/_layouts/default.html

@@ -28,7 +28,7 @@
   <header class="navbar navbar-dark navbar-expand bg-dark flex-md-nowrap p-0 shadow sticky-header">
     <a class="navbar-brand col-sm-3 col-md-2 mr-0" href="/">{{ site.title }}</a>
     <form class="w-100 d-none d-md-flex" action="/search" method="get">
-      <input class="form-control form-control-dark" type="text" placeholder="Search" aria-label="Search" name="q">
+      <input id="search-form" class="form-control form-control-dark" type="text" placeholder="Search" aria-label="Search" name="q">
     </form>
 
     <ul class="navbar-nav flex-row ml-md-auto d-none d-md-flex px-1">