<style type="text/css">
#aviso{
width:500px; /* Largura */
padding:5px; position:absolute; z-index:5000;}
.caja-aviso{
border:4px double #0080FF; /* Cor da borda */
-webkit-border-radius: 10px; -moz-border-radius: 10px; border-radius: 10px; -webkit-box-shadow: 8px 8px 6px #808080; -moz-box-shadow: 8px 8px 6px #808080; box-shadow: 8px 8px 6px #808080;
background-color: #CEECF5; /* Cor de fundo */
padding: 10px; font-family: Verdana, Geneva, sans-serif;
color: #0B173B; /* Cor do texto */
}
.letrero-aviso { /* Estilos da palavra AVISO */
font-size:18pt;
font-weight:bold;
color:#B4045F;
text-shadow: 0px 0px 10px #BA55D3;}
</style>
<div id="aviso" style="left:300px; top:100px; padding:0;">
<div align="right" style="margin-bottom:-30px;"><b><a href="javascript:closeit()" ><font face="Arial" size="1">[FECHAR]</font> <img valign="middle" src="http://i1316.photobucket.com/albums/t609/Multfocos/CloseIcon-small_zpsqpu9rdmv.png" style="vertical-align:middle;"/></a></b></div>
<br/>
<fieldset class="caja-aviso">
<legend class="letrero-aviso" align="center">AVISO</legend>
...Aquí vai sua mensagem...
<br/><div align="right"><a href="http://www.facebook.com/usuario" target="blank"><img src="http://i1316.photobucket.com/albums/t609/Multfocos/facebook%2064x64_zpsbrowhzit.png" width="26"/></a>
<a href="http://twitter.com/usuario" target="blank"><img src="http://i1316.photobucket.com/albums/t609/Multfocos/twiteer64x64_zps0v9jpwfc.png" width="25"/></a></div>
</fieldset>
<script>
function closeit(){
document.getElementById("aviso").style.visibility = "hidden";
}
</script>
</div><div class="clear"/></div>