The new dark gui was hard to look at.
This thread gave me the idea to finally fix it.

Current Features:

• light grey icon backgrounds everywhere
• option to enable/disable shadow under icons
• replaced dark rubber tiles with inventory background in crafting and logistics windows
• increased size of crafting category icons
• red background for locked slots
• uniform button sounds
• supports flib prototypes

Limitations:

• All these changes have to be made at startup to style prototypes. Factorio sadly does not allow users to set individual skins.