Configuration Request: Heavier Lines Between Messages in Inbox

[EndUser]

The lines dividing the messages in the Inbox are so faint, it can be hard to associate senders with subjects... see attachment.

Is there a way to increase intensity (preferred) or even change the color?

Thanks for any tips!

[JohnDoh]

From Elastic skin readme:

- Skin color palette changes and other css modifications can be done
  via _styles.less and _variables.less files. Where you can overwrite all
  variables and add custom styles.