add CSS and JavaScript code to alert message section in header.html.

templates/layouts/header.html

@@ -96,8 +96,17 @@
 
 <div id="fe-main">
     {% if alert %}
-    <div class="be-alert-container">
+    <div class="be-alert-container"
+	 id="be-alert-container">
 	{{alert | safe}}
+	<button class="be-gui-button-no-text"
+		       title="Click to close alert message"
+		       type="button"
+		       id="be-close-alert"
+		       onclick="closeAlert()">
+	    <img alt="Close alert"
+		 src="/images/icons/cross-circle.png">
+	</button>
     </div>
     {% endif %}