site: warning banner: make it more visible

This uses a black background and white text which is the opposite of
the default theme. By using black and white, this also makes sure that
color blind people can still see the banner.

Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org>
Acked-by: Adrien 'neox' Bourmault <neox@gnu.org>

site/template.include

@@ -15,6 +15,15 @@ $if(keywords)$
 $endif$
   <title>$if(title-prefix)$$title-prefix$ – $endif$$pagetitle$</title>
 <style type="text/css">
+
+.warning_banner {
+	background:#000000;
+	color:#ffffff;
+	margin:0 auto;
+	font-family:sans-serif;
+	line-height:5
+}
+
 html{
 	background:#fff;
 	color:#222;
@@ -104,6 +113,7 @@ $endif$
 <hr/>
 $if(x-reviewed)$
 $else$
+<div class="warning_banner">
 <p>
   The information on this page could be outdated or refer to other
   boot software related projects instead of GNU Boot. We also need
@@ -113,6 +123,7 @@ $else$
   page for more details on how to contribute to GNU Boot.
 </p>
 <hr/>
+</div>
 $endif$
 </header>
 $endif$