Tooltip for control sites batch

frontend/src/main/resources/templates/batch.html

@@ -11,6 +11,7 @@
     <link rel="stylesheet" media="screen" href="../static/css/batch.css" th:href="@{/css/batch.css}"/>
 
     <script src="/js/jquery-1.12.0.min.js" th:href="@{/js/jquery-1.12.0.min.js}"></script>
+    <script src="/js/popper.js" th:href="@{/js/popper.js}"></script>
     <script src="/js/bootstrap.min.js" th:href="@{/js/bootstrap.min.js}"></script>
     <script src="/js/plotly-latest.min.js" th:href="@{/js/plotly-latest.min.js}"></script>
     <script src="/js/d3.min.js" th:href="@{/js/d3.min.js}"></script>
@@ -56,7 +57,12 @@
 
                         <p>
                             <label for="background" class="head">Control sites</label>
+
                             <span style="color: red;">*</span>
+
+                            <a class="right" title="" data-placement="right" data-toggle="tooltip" href="#"
+                               data-original-title="A random background will be created when no background sites are uploaded">&#10068;</a>
+
                             <br>
                             <input type="file" id="background" name="background" multiple="multiple"/>
                         </p>
@@ -231,6 +237,9 @@
 </body>
 
 <script>
+    $('a').tooltip();
+
+
     let e = document.getElementById("cellline");
     let hid = document.getElementById("hidden");