Tables and <hr> are nearly black on black and hard to see

[jammons]

I fixed the <hr> issue with this CSS if it's helpful.

.markdown-source-view hr {
  border: none;
  border-top: 1px solid;
  border-color: #828bb8; /* claire de lune table color */
}}

It looks like #57 is trying to solve this same issue for <hr> tags.

Thanks for the great theme!