Problema con CSS

Como lo puedo arreglar?

CSS:
.boton {
color:#000;
font-weight:bolder;
text-decoration:none;
background:#9CD941;
border:1px solid #D0F29D;
border-right-color:#398A38;
border-bottom-color:#398A38;
padding:10px 15px;
font-size:14px;
margin-right:3px;
-moz-border-radius: 20px;
-khtml-border-radius: 20px;
-webkit-border-radius: 20px;
border-radius: 20px;
}
php:
<div>
<div class="alignleft"><span class="boton"><?php next_posts_link('&laquo; Entradas Antiguas') ?></span></div>
<div class="alignright"><span class="boton"><?php previous_posts_link('Entradas nuevas &raquo;') ?></span></div>
</div>