Missing style classes for .own and code-colors

[Krophil]

Thank you for this ! It's really useful to avoid complete white page in Rocket Chat.

However, there was some classes missing which were quiet useful in my case (I don't know which rocket version my company uses so I'm not sure it's for everyone).

For code-colors, I added this to have a darker color on highlighted words

.hljs-keyword, .hljs-selector-tag, .hljs-subst {
    color: #777;
    font-weight: 700;
}

For .own messages, I added this because every message of my own was light :

.own, .own .body {
    background-color: var(--color-dark);
}

And for tags:

.message .title .role-tag {
    background-color: var(--color-light);
}

I didn't make a PR because I think this is not the best colors to change.

Thank you !