Remove the Summit CFP banner now that it is closed

Today marks the official end of the 2023 OpenInfra Summit CFP, so we
can remove the banner promoting it. This mostly reverts
f5e065fe71 but leaves some of the CSS
in place in order to support easier addition and removal of banner
content in the future. Ideally we'd find a balance where we don't
need further CSS edits, but...

Change-Id: I2295eac28ce4e2e47ad8f3a280dd6a4c2e41f849

www/assets/css/main.css

@@ -1943,8 +1943,12 @@ input[type="button"],
       margin-left: 1em;
       margin-top: 1em; }
   #banner header {
+    position: absolute;
+    bottom: 30%;
+    left: 0;
+    width: 100%;
     color: #071d49;
-    margin: 6%; }
+    padding: 1.5em 0; }
     #banner header h2 {
       display: inline-block;
       margin: 0;
@@ -2327,7 +2331,7 @@ input[type="button"],
 
   /* Banner */
   #banner {
-    height: auto; }
+    height: 18em; }
 
   /* Wrapper */
   .wrapper {
@@ -2368,7 +2372,7 @@ input[type="button"],
 
   /* Banner */
   #banner {
-    height: auto; }
+    height: 20em; }
     #banner header {
       padding: 20px; }
 

www/index.html

@@ -72,17 +72,6 @@
 
       <!-- Banner -->
         <section id="banner">
-          <p>
-            <strong>OpenInfra Summit Vancouver Call for Presentations is now
-                Open!</strong>
-            <br/>
-            The OpenInfra Summit Vancouver is the Zuul community’s chance to
-            highlight the open source innovation around Project Gating and
-            CI/CD.
-            <br/>
-            <a href="https://www.openinfra.dev/summit/vancouver-2023"
-              class="button">Submit Your Presentation</a>
-          </p>
           <header>
             <h2>Stop Merging Broken Code</h2>
           </header>