It keeps changing with the needs of the site, so I generally keep it on my scratchpad, but here's a snapshot of the important parts.

Set your theme to "Dark theme", and add this to CSS settings:

/* css for ambrus in perlmonks.com */
/* color, supplementing the Dark theme */
input, textarea, select { background-color: #000000; color: #cccccc }
input[type="submit"] { background-color: #000000; color: #ffffff }
a:link { color: #8080ff }
a:visited { color: #a060d0 }
/* posts */
div.notetext { font-size: 100% }
tr.reply-body ul.indent font[size="2"] { font-size: 100% }
div.readmore { background-color: transparent; padding-left: 2px; borde
+r-left-width: 2px; border-left-color: #080; border-left-style: solid 
+}
/* nodelets */
tbody.nodelet td { font-size: 100%; background-color: #000000 }
#XP_Nodelet sup { vertical-align: text-top }
/* cb messages */
tbody.nodelet td.highlight { /* background-color: transparent */ }
tr.cb_msg td, tr.cb_me td { padding: 0px; text-indent: -0.6em; padding
+-left: 0.6em; }
/* cb speakers: */
span.chat span.cb_author *:link, span.chat span.cb_author *:visited { 
+font-size: 111% }
span.chat i > span.cb_author *:link , span.chat i > span.cb_author *:v
+isited { font-size: 111%; font-style: italic }
/* cb separators
span.chat span.cb_author:before { content: "\3d" }
span.chat i > span.cb_author:before { content: "\3d" }
span.chat span.cb_author:after { content: "\3d" }
span.chat i > span.cb_author:after { content: "" }
*/
span.chat span.cb_sq_br:first-child , span.chat  span.cb_sq_br , span.
+chat span.cb_me_bullet   { display: none }
/* span.chat span.cb_sep { } */
/* cb sidebar */
body#id-481185 input[name="message"] { width: 100%; }
body#id-481181 table.cb_table td { font-size: 17px }
/* increase some text areas */
*.user-settings textarea[name="setstyle"] { width: 80ex; height: 20em 
+}
/* misc */
div.ss-criteria-summary { display: none }
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