Your custom CSS is a mess. I tried to clean it up and the result is below.
Please replace your CSS with the one below and change what you think is wrong.
.nabble,
.nabble table,
.nabble .info-message th,
.nabble .message-text, .small,
.nabble .editor-table td, p, form,
small, ul, table td, .breadcrumbs {
color: #888;
}
#nabble.path {color:#888;}
.nabble h1, .nabble h2, .nabble .light-black {
color: #ccc;
}
.nabble a:hover {
color: #66CCFF;
text-decoration: underline;
}
a:hover {color: #3366CC; text-decoration: underline; }
span.dropdown table {
background-color:#333;
border-color:#222;
}
span.dropdown-item {
color:#999;
}
tr.dropdown-hover {
color:#bbb;
background-color:#444444;
}
.nabble a:link {
color: #95ABB8;
text-decoration: none;
}
.nabble a:visited {
color: #FFF;
text-decoration: none;
}
.nabble a:hover {
color: #3366CC
text-decoration: underline;
}
body, .nabble, .nabble .no-bg-color {
background-color: #222222;
}
.nabble .light-bg-color { background-color: #333; color:#777;}
.nabble .shaded-bg-color { background-color: #444; color:#777; }
.nabble th, .nabble .dark-bg-color { background-color: #555; color:#777;}
.nabble .error-message, .nabble .info-message, .nabble .light-highlight { background:#23393F; }
.nabble .highlight { background-color: #596B70; }
.nabble .info-message th, .nabble .dark-highlight { background-color: #1A505E; }
.nabble table, .nabble li, .nabble div, .nabble .medium-border-color { border-color: #999; }
.nabble td, .nabble .light-border-color { border-color: #777; }
.nabble .dark-border-color { border-color: #aaa; }
.nabble .error-message { border-color: #9CB7C8; }
.nabble .info-message { border-color: #3366ff; }
.post-border, td.post-border { border-color: #CCCCCC; }
span.post-date { color: #7F8151; }
span.post-author { color:#566A76; }
span.post-snippet { color: #ccc; }
span.post-subject { color: #ddd; }
.post-hover { background-color:#444}
select, input, textarea, button { border:1px solid #555; background: #333; color: #999;}
input[type=radio] { border:none; background: #333; color:#999;}
span.connect-line, span.connect-end { background-image:url("/images/styles/connect-line.gif"); }
td.connect-end { background-image:url("/images/styles/connect-end.gif"); }
td.connect-node { background-image:url("/images/styles/connect-node.gif"); }