I´m new in this html and css world, and this is my first big problem, i've no idea how to solve it, it would be great if someone knows the solution.

This is how it looks now:


This is how it should look like:


This is the code:
Code:
HTML

<fieldset id="formulario">
                	<legend>HABITACIONES Y TARIFAS</legend>
                    <label for="check-in">Fecha de Check-in</label><br />
                    <div class="campos">
						<input name="check-in_dia" id="check-in_dia" type="text" value="Dia" size="9" maxlength="3">
                    	<input name="check-in_mes" id="check-in_mes" type="text" value="Mes" size="9" maxlength="3">
                    	<input name="check-in_año" id="check-in_año" type="text" value="Año" size="9" maxlength="4"><br />
                    </div>
                    <label for="check-out">Fecha de Check-out</label><br />
					<div class="campos">	
                        <input name="check-out_dia" id="check-out_dia" type="text" value="Dia" size="9" maxlength="3">
                   		<input name="check-out_mes" id="check-out_mes" type="text" value="Mes" size="9" maxlength="3">
                    	<input name="check-out_año" id="check-out_año" type="text" value="Año" size="9" maxlength="4"><br />
                    </div>
                    <div id="bloque_campo_izq">
                        <label for="habitaciones">Habitaciones</label><br />
                        <div class="campos">	
                            <input name="habitaciones" id="habitaciones" type="text" value="1" size="4" maxlength="2">   
                        </div>
                    </div>
                    <div class="bloque_campos_der">         
                        <label for="niños">Niños</label><br />
                        <div class="campos">
                            <input name="niños" id="niños" type="text" value="1" size="4" maxlength="2">   
                        </div> 
                    </div>
                    <div class="bloque_campos_der">
                        <label for="adultos">Adultos</label><br />
                        <div class="campos">
                            <input name="adultos" id="adultos" type="text" value="1" size="4" maxlength="2">
                    	</div>  
                    </div><br />
                    <a href="buscar.html" id="buscar">BUSCAR</a>  
                </fieldset>
Code:
CSS

#formulario{
	width:287px;
	height:280px;
	border:none;
	float:left;
	background-color:#152773;
	font-size:12px;
	margin-left:77px;
	}
	
	
#formulario legend{
	font-size:18px;
	text-align:center;
	border-bottom:solid 2px;
	}
	
#formulario label, #formulario input{
	float:left;
	border:none;
	}
	
#formulario label{
	padding-left:42px;
	}
	
.campos{
	padding-left:35px;
	}
	
#formulario input{
	color:#999;
	margin-left:9px;
	padding-left:5px;
	}
	
#bloque_campo_izq{
	display:block;
	float:left;
	}
	
.bloque_campos_der{
	float:left;
	width:50px;
}

#buscar{
	float:left;
	margin-top:20px;
	text-align:center;
	text-decoration:none;
	color:#b60718;
	width:110px;
	height:20px;
	background-color:#fff;
	font-size:14px;
	margin-left:90px;
	margin-top:33px;
	}
Thanks for reading.