Buenas!
En este post les explicare paso a paso como instalar la modificación que hice al Tema 2.0 de este foro, para que quede asi
Primero, deben instalarse Stylish, es una extension que permite modificar el CSS "en vivo" al navegar.
Descargar para Firefox
Descargar para Chrome / Chromium
Luego deben elejirse el tema 2.0 en el foro. Para eso, van a Perfil y en en el panel de la derecha, ponen "Configuración de Apariencia y Diseño" y en Tema Actual, Elegir "Tema 2.0" (presionando el boton "cambiar" y haciendo click en el nombre del tema)

Luego agregan mi estilo al Stylish
Para Firefox:
Van a la esquina inferior derecha donde hay una "S" blanca, le hacen click y ponen "Administrar estilos", y presionan "Escribir nuevo estilo". Les saldra un nuevo dialogo, ponen el nombre que quieran ("elHacker.net Dark Style" para este caso
), y en el codigo ponen lo siguiente, aceptan y listo!
Para Chrome:
Hagan click derecho en la "S" que aparece al lado de la barra de URL (omnibar) y ponen opciones, clickean en "Add new style". Le ponen un nombre, con Enabled Activado. En la parte de "Applies To" presionan "Especify" y seleccionan "URL starting with" poniendo la url del foro, con el protocolo que usen (HTTP o HTTPS). Deberia quedar "http://foro.elhacker.net" (en mi caso) y en codigo ponen el codigo de mas abajo y ponen "save" y listo
Ahora si, si hicieron todo bien, los cambios ya deberian verse (o al menos presionen F5 para actualizar)
Espero que les sirva y que mas de uno lo use!
Si alguno tiene problemas, pondre imagenes
En este post les explicare paso a paso como instalar la modificación que hice al Tema 2.0 de este foro, para que quede asi
Citar
Indice
Como se veria un foro
Este post
Mi perfil
Encuesta EHN-DEV 2010
Un tema con bastante codigo (El geshi no lo puedo modificar)
Respondiendo un post
Primero, deben instalarse Stylish, es una extension que permite modificar el CSS "en vivo" al navegar.
Descargar para Firefox
Descargar para Chrome / Chromium
Luego deben elejirse el tema 2.0 en el foro. Para eso, van a Perfil y en en el panel de la derecha, ponen "Configuración de Apariencia y Diseño" y en Tema Actual, Elegir "Tema 2.0" (presionando el boton "cambiar" y haciendo click en el nombre del tema)

Luego agregan mi estilo al Stylish
Para Firefox:
Van a la esquina inferior derecha donde hay una "S" blanca, le hacen click y ponen "Administrar estilos", y presionan "Escribir nuevo estilo". Les saldra un nuevo dialogo, ponen el nombre que quieran ("elHacker.net Dark Style" para este caso

Código [Seleccionar]
@-moz-document url-prefix('https://foro.elhacker.net') {
img[src="https://foro.elhacker.net/Themes/newgeneration/images/on.gif"]{height: 0 !important; width: 0 !important; padding-left: 50px !important; padding-top: 34px !important; background: url('http://img810.imageshack.us/img810/2725/30970175.png') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/on2.gif"]{height: 0 !important; width: 0 !important; padding-left: 50px !important; padding-top: 34px !important; background: url('http://img130.imageshack.us/img130/4936/on2a.png') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/off.gif"]{height: 0 !important; width: 0 !important; padding-left: 50px !important; padding-top: 36px !important; background: url('http://img821.imageshack.us/img821/3663/offi.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/normal_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img17.imageshack.us/img17/7943/normalpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/hot_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img153.imageshack.us/img153/3956/hotpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/veryhot_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img838.imageshack.us/img838/7171/veryhotpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/my_normal_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img684.imageshack.us/img684/57/mynormalpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/my_hot_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img651.imageshack.us/img651/4724/myhotpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/my_veryhot_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img337.imageshack.us/img337/5421/myveryhotpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/post/xx.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img585.imageshack.us/img585/8227/32131385.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/post/exclamation.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img249.imageshack.us/img249/2711/exclamation.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/post/question.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background:url('http://img214.imageshack.us/img214/4929/questionv.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/poll_left.gif"]{height: 0 !important; width: 0 !important; padding-left: 6px !important; padding-top: 12px !important; background: url('http://img713.imageshack.us/img713/8357/pollleft.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/poll_middle.gif"]{content: url('http://img337.imageshack.us/img337/425/pollmiddle.gif') !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/poll_right.gif"]{height: 0 !important; width: 0 !important; padding-left: 6px !important; padding-top: 12px !important; background: url('http://img707.imageshack.us/img707/9328/pollrightn.gif') no-repeat !important;}
*#hora{color:#FFF !important;}
#shadow-l{background:url('http://img130.imageshack.us/img130/1262/shadowld.png')!important}
#shadow-r{background:url('http://img233.imageshack.us/img233/5595/shadowrz.png')!important}
#mainbody{background:#222 !important}
a img{border:none !important}
.quote{color:#222 !important; background-color:#AAA !important; border:1px solid #232833 !important;}
.quote a{color:#444 !important}
.code{color:#111 !important; background-color:#DDD !important; border:1px solid #000 !important;}
.quoteheader, .codeheader{color:#EEE !important;}
.highlight{background-color:yellow !important; font-weight:bold !important; color:black !important}
.windowbg, tr.windowbg td{background:#444 !important; border-bottom:1px solid #555 !important}
.windowbg2, tr.windowbg2 td{background:#333 !important}
.windowbg3, tr.windowbg3 td{background:#222 !important}
.calendar_today{}
table.nopad .titlebg, tr.titlebg th, tr.titlebg td, table .titlebg2, tr.titlebg2 th, tr.titlebg2 td, tr td.titlebg{color:#FFF !important; background: url('http://img141.imageshack.us/img141/5024/navbgs.png') #DDC repeat-x !important;}
.titlebg, .titlebg a:link, .titlebg a:visited{color:#CCC !important;}
.titlebg2 a{color:#CCC !important;}
.titlebg a:hover{color:#FFF !important;}
.titlebg, .titlebg2{background:#444 !important;}
.bordercolor{ border:1px solid #000 !important;}
.tborder{ border:2px solid #000 !important;}
.catbg, .catbg2{color:#fff !important; background:#232833 url('http://img141.imageshack.us/img141/5024/navbgs.png') repeat-x !important; border-bottom:1px solid #000 !important;}
.catbg3{color:#FFF !important; background:url('http://img141.imageshack.us/img141/5024/navbgs.png') !important;}
.catbg3 a{color:#FFF !important; text-decoration:none !important;}
.catbg a, .catbg2 a, .catbg a:hover, .catbg2 a:hover{color:#fff !important; text-decoration:none !important;}
.catbg a img, .catbg2 a img, .catbg3 a img{border:none !important;}
.smalltext a{color:#DDD !important; text-decoration:none !important;}
.smalltext a img, .smalltext a:hover img{border:0 !important;}
.smalltext a:hover{color:#777 !important; border-bottom:solid 1px #777 !important;}
.signature a img{border:none !important; text-decoration:none}
.error{color:red}
#header{background:url('http://img408.imageshack.us/img408/8404/headerbgb.png') repeat-x !important;}
#header-l{background:url('http://img714.imageshack.us/img714/8087/headerla.png') 0 0 no-repeat !important;}
#header-r{background:url('http://img715.imageshack.us/img715/1386/headerreh.png') 100% 0 no-repeat !important; }
#logo-bg, #logo-bg a{background:url('http://img221.imageshack.us/img221/7074/logobg.png') no-repeat !important;}
#logo, #logo a{background:url('http://img151.imageshack.us/img151/3576/logomy.png') no-repeat !important;}
#news{background-color:#444 !important; border:1px solid #ccc !important;}
div.profile_info{color:#000 !important}
div.profile_info a{color:#222 !important}
div.profile_info a:hover{color:#000 !important}
#toolbar{background:url('http://img708.imageshack.us/img708/9389/navbg2.png') repeat-x !important}
#nav{color:#FFF !important; background:url('http://img141.imageshack.us/img141/5024/navbgs.png') !important;}
#nav li a{color:#FFF !important}
#nav a:hover{background:url('http://img708.imageshack.us/img708/9389/navbg2.png') !important}
#showcase{background:#fff !important; color:#444 !important;}
#footer{background:url('http://img40.imageshack.us/img40/8987/footerbgd.png') repeat-x !important; color:#eee !important;}
#footer-l{background:url('http://img208.imageshack.us/img208/5641/footerbgl.png') 0 0 no-repeat !important; padding-left:20px !important;}
#footer-r{background:url('http://img263.imageshack.us/img263/4379/footerbgr.png') 100% 0 no-repeat !important; height:83px; padding-right:20px !important;}
#footer a{ color:#000 !important}
#footer a:hover{color:#CCC !important}
#footer2{color:#999 !important}
body{color:#E7E7E7 !important}
#page_bg{background:#252525 !important;}
a{color:#BBB !important; outline:none !important}
a:hover{color:#FFF !important; text-decoration:none !important}
a:link,a:visited{text-decoration:none !important}
a:hover{text-decoration:none !important}
h1{padding-bottom:5px}
h2{padding-bottom:5px}
h3{padding-bottom:0px}
h4{padding-bottom:5px}
.small{color:#999 !important}
.createdate,.modifydate{color:#999 !important}
#ajax_in_progress{background:#444; color:white; text-align:center; font-weight:bold; font-size:18pt; padding:3px; width:100%; position:fixed; top:0; left:0}
.geshi{color:#111 !important; background-color:#DDD !important; border:1px solid #222 !important;}
}
Para Chrome:
Hagan click derecho en la "S" que aparece al lado de la barra de URL (omnibar) y ponen opciones, clickean en "Add new style". Le ponen un nombre, con Enabled Activado. En la parte de "Applies To" presionan "Especify" y seleccionan "URL starting with" poniendo la url del foro, con el protocolo que usen (HTTP o HTTPS). Deberia quedar "http://foro.elhacker.net" (en mi caso) y en codigo ponen el codigo de mas abajo y ponen "save" y listo

Código [Seleccionar]
img[src="https://foro.elhacker.net/Themes/newgeneration/images/on.gif"]{height: 0 !important; width: 0 !important; padding-left: 50px !important; padding-top: 34px !important; background: url('http://img810.imageshack.us/img810/2725/30970175.png') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/on2.gif"]{height: 0 !important; width: 0 !important; padding-left: 50px !important; padding-top: 34px !important; background: url('http://img130.imageshack.us/img130/4936/on2a.png') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/off.gif"]{height: 0 !important; width: 0 !important; padding-left: 50px !important; padding-top: 36px !important; background: url('http://img821.imageshack.us/img821/3663/offi.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/normal_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img17.imageshack.us/img17/7943/normalpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/hot_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img153.imageshack.us/img153/3956/hotpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/veryhot_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img838.imageshack.us/img838/7171/veryhotpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/my_normal_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img684.imageshack.us/img684/57/mynormalpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/my_hot_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img651.imageshack.us/img651/4724/myhotpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/topic/my_veryhot_post.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img337.imageshack.us/img337/5421/myveryhotpost.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/post/xx.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img585.imageshack.us/img585/8227/32131385.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/post/exclamation.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background: url('http://img249.imageshack.us/img249/2711/exclamation.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/post/question.gif"]{height: 0 !important; width: 0 !important; padding-left: 20px !important; padding-top: 20px !important; background:url('http://img214.imageshack.us/img214/4929/questionv.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/poll_left.gif"]{height: 0 !important; width: 0 !important; padding-left: 6px !important; padding-top: 12px !important; background: url('http://img713.imageshack.us/img713/8357/pollleft.gif') no-repeat !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/poll_middle.gif"]{content: url('http://img337.imageshack.us/img337/425/pollmiddle.gif') !important;}
img[src="https://foro.elhacker.net/Themes/newgeneration/images/poll_right.gif"]{height: 0 !important; width: 0 !important; padding-left: 6px !important; padding-top: 12px !important; background: url('http://img707.imageshack.us/img707/9328/pollrightn.gif') no-repeat !important;}
*#hora{color:#FFF !important;}
input, textarea, select{border:#222 1px solid !important;color:#FFF !important;background-color:#666 !important;}
#shadow-l{background:url('http://img130.imageshack.us/img130/1262/shadowld.png')!important}
#shadow-r{background:url('http://img233.imageshack.us/img233/5595/shadowrz.png')!important}
#mainbody{background:#222 !important}
a img{border:none !important}
.quote{color:#222 !important; background-color:#AAA !important; border:1px solid #232833 !important;}
.quote a{color:#444 !important}
.code{color:#111 !important; background-color:#DDD !important; border:1px solid #000 !important;}
.quoteheader, .codeheader{color:#EEE !important;}
.highlight{background-color:yellow !important; font-weight:bold !important; color:black !important}
.windowbg, tr.windowbg td{background:#444 !important; border-bottom:1px solid #555 !important}
.windowbg2, tr.windowbg2 td{background:#333 !important}
.windowbg3, tr.windowbg3 td{background:#222 !important}
.calendar_today{}
table.nopad .titlebg, tr.titlebg th, tr.titlebg td, table .titlebg2, tr.titlebg2 th, tr.titlebg2 td, tr td.titlebg{color:#FFF !important; background: url('http://img141.imageshack.us/img141/5024/navbgs.png') #DDC repeat-x !important;}
.titlebg, .titlebg a:link, .titlebg a:visited{color:#CCC !important;}
.titlebg2 a{color:#CCC !important;}
.titlebg a:hover{color:#FFF !important;}
.titlebg, .titlebg2{background:#444 !important;}
.bordercolor{ border:1px solid #000 !important;}
.tborder{ border:2px solid #000 !important;}
.catbg, .catbg2{color:#fff !important; background:#232833 url('http://img141.imageshack.us/img141/5024/navbgs.png') repeat-x !important; border-bottom:1px solid #000 !important;}
.catbg3{color:#FFF !important; background:url('http://img141.imageshack.us/img141/5024/navbgs.png') !important;}
.catbg3 a{color:#FFF !important; text-decoration:none !important;}
.catbg a, .catbg2 a, .catbg a:hover, .catbg2 a:hover{color:#fff !important; text-decoration:none !important;}
.catbg a img, .catbg2 a img, .catbg3 a img{border:none !important;}
.smalltext a{color:#DDD !important; text-decoration:none !important;}
.smalltext a img, .smalltext a:hover img{border:0 !important;}
.smalltext a:hover{color:#777 !important; border-bottom:solid 1px #777 !important;}
.signature a img{border:none !important; text-decoration:none}
.error{color:red}
#header{background:url('http://img408.imageshack.us/img408/8404/headerbgb.png') repeat-x !important;}
#header-l{background:url('http://img714.imageshack.us/img714/8087/headerla.png') 0 0 no-repeat !important;}
#header-r{background:url('http://img715.imageshack.us/img715/1386/headerreh.png') 100% 0 no-repeat !important; }
#logo-bg, #logo-bg a{background:url('http://img221.imageshack.us/img221/7074/logobg.png') no-repeat !important;}
#logo, #logo a{background:url('http://img151.imageshack.us/img151/3576/logomy.png') no-repeat !important;}
#news{background-color:#444 !important; border:1px solid #ccc !important;}
div.profile_info{color:#000 !important}
div.profile_info a{color:#222 !important}
div.profile_info a:hover{color:#000 !important}
#toolbar{background:url('http://img708.imageshack.us/img708/9389/navbg2.png') repeat-x !important}
#nav{color:#FFF !important; background:url('http://img141.imageshack.us/img141/5024/navbgs.png') !important;}
#nav li a{color:#FFF !important}
#nav a:hover{background:url('http://img708.imageshack.us/img708/9389/navbg2.png') !important}
#showcase{background:#fff !important; color:#444 !important;}
#footer{background:url('http://img40.imageshack.us/img40/8987/footerbgd.png') repeat-x !important; color:#eee !important;}
#footer-l{background:url('http://img208.imageshack.us/img208/5641/footerbgl.png') 0 0 no-repeat !important; padding-left:20px !important;}
#footer-r{background:url('http://img263.imageshack.us/img263/4379/footerbgr.png') 100% 0 no-repeat !important; height:83px; padding-right:20px !important;}
#footer a{ color:#000 !important}
#footer a:hover{color:#CCC !important}
#footer2{color:#999 !important}
body{color:#E7E7E7 !important}
#page_bg{background:#252525 !important;}
a{color:#BBB !important; outline:none !important}
a:hover{color:#FFF !important; text-decoration:none !important}
a:link,a:visited{text-decoration:none !important}
a:hover{text-decoration:none !important}
h1{padding-bottom:5px}
h2{padding-bottom:5px}
h3{padding-bottom:0px}
h4{padding-bottom:5px}
.small{color:#999 !important}
.createdate,.modifydate{color:#999 !important}
#ajax_in_progress{background:#444; color:white; text-align:center; font-weight:bold; font-size:18pt; padding:3px; width:100%; position:fixed; top:0; left:0}
.geshi{color:#111 !important; background-color:#DDD !important; border:1px solid #222 !important;}
Ahora si, si hicieron todo bien, los cambios ya deberian verse (o al menos presionen F5 para actualizar)
Espero que les sirva y que mas de uno lo use!
Si alguno tiene problemas, pondre imagenes
