It's not a plugin, simple HTML and CSS.
An example would be:
CSS Code (to add in global.css)
.announcement_1, .announcement_2 {
text-align: center;
padding: 8px;
-webkit-border-radius: 5px;
-moz-border-radius: 5px;
border-radius: 5px;
border-style: solid;
border-width: 1px;
margin: 5px;
}
.announcement_1 {
background: #FFF3A6;
border-color: #F7CD26;
}
.announcement_2 {
background-color: #D6EDA2;
border-color: #80C02C;
}
HTML Code (index template or wherever you want it to appear)
<div class="announcement_1">
<strong>Announcement 1:</strong> content of my announcement
</div>
<div class="announcement_2">
<strong>Announcement 2:</strong> content of my announcement
</div>
Demo:
http://jsfiddle.net/mxvu1b3y/