Decoration: make outline more outliney
The current outline is so subtle as to be almost invisible even with Breeze Dark, and actually invisible (by design) on Breeze Light. Thus it doesn't serve its purpose of being an outline that well.
This commit makes it more contrasty, so that it's an actual outline more of the time. Also, by being darker with a light color scheme, the someewhat awkward contrast when using a dark terminal color scheme is substantially reduces to the "I don't mind it anymore" territory, IMO.
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