Listas horizontales adaptables con elementos centrados – programmers

Hoy toca lo que en el argot de programación se denomina con el vocablo ingléssnippet, o lo que es lo mismo, un pequeño trozo de código que podemos reutilizar para distintos programas. En ocasiones esta definición también encajaría para el términorutina, que es lo que por ejemplo sería un sistema para mostrar fechas en un formato determinado o una líneas que convirtieran números en cadenas.

Sin embargo, cuando hablamos de CSS lo más habitual es que nos estemos refiriendo a pequeños trucos que resuelven problemas concretos pero comunes a muchos diseños.

Eso es lo que veremos hoy, un sistema sencillo de formatear una lista para que se vea en horizontal y que además sus elementos estén totalmente centrados con respecto a sus márgenes laterales.

Normalmente esto se usa para crear menús y el truquillo nos servirá no sólo para que sus elementos estén centrados, sino para que SIEMPRE estén centrados, independientemente del ancho de la ventana. Es decir, que sean adaptables (RWD, Responsive Web Design).

Lo habitual

Supongamos este HTML para formar una lista:

ul class="lista"
lia href="#"UNO/a/li
lia href="#"DOS/a/li
lia href="#"TRES/a/li
lia href="#"CUATRO/a/li
/ul

Si a modo de muestreo, miráis en el código fuente de unos cuantos menús, descubriréis que muchísimos de ellos utilizanfloat para conseguir acomodar los elementos de la lista uno junto a otro. Este sería un CSS típico y a continuación el resultado:

ul.lista {width:100%; border-top: 1px solid blue;}
ul.lista li {float:left; margin: 0 4px 0 0; list-style:none;}
ul.lista li a {display:block; text-decoration:none; padding: 4px; border-bottom: 4px solid transparent; color: black;}
ul.lista li a:hover {color: blue; border-color: blue;}

• UNO
• DOS
• TRES
• CUATRO

El problema de usarfloat está a la vista y es que todo se nos va a la izquierda de la caja contenedora (en este ejemplo el cuerpo para posts).

Además no nos podemos olvidar de situar unclear tras la lista. Caso contrario lo siguiente que aparezca en la página se acoplará al último elemento descuadrándonos todo.


Pues bien, para centrar eso no queda otra que darle un ancho determinado a la lista (ul) y añadir unmargin: 0 auto;, pero la cuestión es que eso sólo se puede hacer cuando cada elemento de lista (li) tiene un ancho conocido y podemos sumarlos para obtener el que debería tener la lista completa.

En el ejemplo anterior podemos calcular el espacio que ocupan los cuatro enlaces por lo que podríamos cambiar esto en el CSS:

ul.lista {width: 230px; margin:0 auto; border-top: 1px solid blue;}

Y ahora sí que tendremos centrada la lista:

• UNO
• DOS
• TRES
• CUATRO

Pero ¿qué ocurre si en el futuro incorporamos un nuevo elemento de lista, cambiamos el tamaño de fuente, el relleno o cualquier otra cosa que haga cambiar el tamaño total? Pues eso, que tendremos que calcular y ajustar de nuevo el ancho de la lista.

La sencilla solución

Para solucionar estos problemillas hay una solución y lo mejor de todo es que es muy simple.

Se trata de utilizar para los elementos de lista undisplay: inline-block (bloques en línea) en lugar defloat y añadir a su caja contenedora, que no es otra que la marcada comoul, untext-align:center. Con eso ya se nos centrará todo automáticamente:

ul.lista {width:100%; border-top: 1px solid blue;text-align: center;}
ul.lista li {display: inline-block; margin: 0 4px 0 0; list-style:none;}
ul.lista li a {display:block; text-decoration:none; padding: 4px; border-bottom: 4px solid transparent; color: black;}
ul.lista li a:hover {color: blue; border-color: blue;}

• UNO
• DOS
• TRES
• CUATRO

Y da igual qué cantidad de elementos haya o qué espacio ocupa cada uno de ellos. Con este código siempre nos quedará todo centrado y tal y como prometía, con un diseño adaptable.

Sólo tenéis que probar a hacer más pequeña la ventana de vuestro navegador y veréis que los elementos pasan a ocupar más líneas, pero que siguen centrados.

• UNO
• DOS
• TRES
• CUATRO
• CINCO
• SEIS
• SIETE
• OCHO
• NUEVE
• DIEZ

Por si estáis interesados, este sería el código para el anterior menú:

ul.lista {font-family:helvetica,arial,sans-serif;margin:0;padding:0;text-align:center;width:100%;font-size:0;}
ul.lista li {list-style: none;display: inline-block;width: 110px;margin:4px 1px;padding: 0;font-size:14px;}
ul.lista li a {display:block;text-decoration:none;padding:0.5em 0.5em;border-left:10px solid #036;border-right:10px solid #036;color:#fff;background:#036;}
ul.lista li a:hover {border-left:10px solid red;border-right:10px solid #369;color:#fff;background:#369;}

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