.letras {
	font-family: Georgia, "Times New Roman", Times, serif;
	font-size: small;
	color: #000000;
}
.letras2 {
	font-family: Georgia, "Times New Roman", Times, serif;
	font-size: 14px;
	color: #863F23;
}
.letrasnegro {
	font-family: Georgia, "Times New Roman", Times, serif;
	font-size: 15px;
	color: #000000;
}
.letras2negras {
	font-family: Georgia, "Times New Roman", Times, serif;
	font-size: 14px;
	color: #000000;
}
.titulonegro {
	font-family: Georgia, "Times New Roman", Times, serif;
	font-size: 18px;
	font-weight: bold;
	color: #000000;
}
.letras10 {
	font-family: Georgia, "Times New Roman", Times, serif;
	font-size: 10px;
	color: #FFFFFF;
}
<div id="superior_izquierda">
   <div id="superior_derecha">
      <div id="inferior_izquierda">
         <div id="inferior_derecha">
            contenido
         </div>
      </div>
   </div>
</div>