jquery: Add an OpenJS World 2021 banner

Closes gh-431

Author: mgol

themes/jquery/css/base.css

@@ -2231,22 +2231,14 @@ p.author a {
 	line-height: 36px;
 }
 
-#banner-blm {
-	background-image: url(../images/dark-grey-tile.png);
-	color: #fff;
-	text-align: center;
-	padding: 20px;
-}
-
-#banner-blm h2 {
-	font-size: 36px;
-	line-height: 42px;
-}
-
-#banner-blm p {
-	font: 22px/26px "Helvetica Neue", Helvetica, Arial, Geneva, sans-serif;
-	padding-left: 15%;
-	padding-right: 15%;
+#banner-openjs-world-2021 {
+	display: block;
+	width: 100%;
+	height: 200px;
+	background-image: url(../images/banner-openjs-world-2021.png);
+	background-position: center center;
+	background-repeat: no-repeat;
+	background-color: #1d2737ff;
 }
 
 .center-txt {

themes/jquery/header.php

@@ -104,10 +104,13 @@
 	</section>
 </header>
 
-<div id="banner-blm">
-	<h2>#BlackLivesMatter</h2>
-	<p>To Donate, see this <a href="https://bit.ly/fundthecommunity">list of organizations to support</a> from <a href="https://www.reclaimtheblock.org/">Reclaim the Block</a> 
-</div>
+<a id="banner-openjs-world-2021" href="https://openjsf.org/openjs-world-2021/">
+	<div class="visuallyhidden">
+		<h2>OpenJS World</h2>
+		<p>June 2, 2021</p>
+		<p>Register today!</p>
+	</div>
+</a>
 
 <div id="container">
 	<div id="logo-events" class="constrain clearfix">