Low visibility of headers in markdown tables

[hugo19941994]

Hi!

Since version 3.3.2 (3.3.1 works fine) the headers of tables inside the response description fields can barely be seen.

I think this behavior changed after commit 2cd4989

Q	A
Bug or feature request?	Bug
Which Swagger/OpenAPI version?	2.0, maybe 3.0
Which Swagger-UI version?	3.3.2+
How did you install Swagger-UI?	Manually
Which browser & version?	Chrome 62
Which operating system?	Linux

Demonstration API definition

400:
  description:
    | Error Code | Description                                          |
    | --------------- | ---------------------------------------------------- |
    | 1                | Missing X-Client-Code request header |

Expected Behavior

Current Behavior

Possible Solution

Can be quickly fixed by changing the layout SCSS file. Just make th white inside .response-col_description__inner

https://github.com/hugo19941994/swagger-ui/commit/9dac9f348400fe859ee7738ea42a433c194b898f

[hugo19941994]

Thanks for taking a look @owenconti !

I realised today that the horizontal bar which separates the headers has bad visibility too. I've sent an alternative PR to yours which also sets the bar to the same color as the text.