It looks like this gets included by TinyMCE so you have to make sure your rules overrule this (or edit it) if you want your styles to come through:
from lib/editor/tinymce/tiny_mce/3.5.1.1/themes/advanced/skins/o2k7/content.
css
Though on my first go at editing it (removing everything not specifically marked .mceWhatever) I couldn't get the changes to register, which reminds me of when I was trying to get editor.css to work in the first place. Anyone know how to force this file to refresh?
A quick Google gave me this:
"Note: updating the actual content.css will have no effect. You need to create a copy and reference it in tinyMCE.init()" Anyone know where to do this for Moodle? I'm guessing that's where you can make all sort of other changes to TinyMCE.
body, td, pre {color:#000; font-family:Verdana, Arial, Helvetica, sans-serif; font-size:10px; margin:8px;}
body {background:#FFF;}
body.mceForceColors {background:#FFF; color:#000;}
h1 {font-size: 2em}
h2 {font-size: 1.5em}
h3 {font-size: 1.17em}
h4 {font-size: 1em}
h5 {font-size: .83em}
h6 {font-size: .75em}
.mceItemTable, .mceItemTable td, .mceItemTable th, .mceItemTable caption, .mceItemVisualAid {border: 1px dashed #BBB;}
a.mceItemAnchor {display:inline-block; width:11px !important; height:11px !important; background:url(../default/img/items.gif) no-repeat 0 0;}
span.mceItemNbsp {background: #DDD}
td.mceSelected, th.mceSelected {background-color:#3399ff !important}
img {border:0;}
table, img, hr, .mceItemAnchor {cursor:default}
table td, table th {cursor:text}
ins {border-bottom:1px solid green; text-decoration: none; color:green}
del {color:red; text-decoration:line-through}
cite {border-bottom:1px dashed blue}
acronym {border-bottom:1px dotted #CCC; cursor:help}
abbr {border-bottom:1px dashed #CCC; cursor:help}
/* IE */
* html body {
scrollbar-3dlight-color:#F0F0EE;
scrollbar-arrow-color:#676662;
scrollbar-base-color:#F0F0EE;
scrollbar-darkshadow-color:#DDD;
scrollbar-face-color:#E0E0DD;
scrollbar-highlight-color:#F0F0EE;
scrollbar-shadow-color:#F0F0EE;
scrollbar-track-color:#F5F5F5;
}
img:-moz-broken {-moz-force-broken-image-icon:1; width:24px; height:24px}
font[face=mceinline] {font-family:inherit !important}
*[contentEditable]:focus {outline:0}
.mceItemMedia {border:1px dotted #cc0000; background-position:center; background-repeat:no-repeat; background-color:#ffffcc}
.mceItemShockWave {background-image:url(../../img/shockwave.gif)}
.mceItemFlash {background-image:url(../../img/flash.gif)}
.mceItemQuickTime {background-image:url(../../img/quicktime.gif)}
.mceItemWindowsMedia {background-image:url(../../img/windowsmedia.gif)}
.mceItemRealMedia {background-image:url(../../img/realmedia.gif)}
.mceItemVideo {background-image:url(../../img/video.gif)}
.mceItemAudio {background-image:url(../../img/video.gif)}
.mceItemIframe {background-image:url(../../img/iframe.gif)}
.mcePageBreak {display:block;border:0;width:100%;height:12px;border-top:1px dotted #ccc;margin-top:15px;background:#fff url(../../img/pagebreak.gif) no-repeat center top;}
.mceHideBrInPre pre br {display: none}