support more keys to refine highlight colors

[dangh]

Problem description

Currently, color schemes only support highlight, find_highlight, find_highlight_foreground to style highlight text.

• highlight is unfocused border
• find_highlight is the focused background
• find_highlight_foreground is the focused text color and border color

There are 2 problems:

• There's no ways to change the focused/unfocused border/background separately
• It's confusing that the find_highlight_foreground, as the name suggested, also affect border color.

This is my color scheme:

It's hard to see but the text color and border color of the focused word has the same color, it's ugly and harmful to legibility as the text is touching the border.

Preferred solution

We can introduce a few new keys to avoid breaking existing color schemes:

• highlight_background: unfocused background color, which is transparent by default
• highlight_border: unfocused border color, fallback to highlight
• find_highlight_background: focused background color, fallback to find_highlight
• find_highlight_border: focused border color, fallback to find_highlight_foreground

Additional Information (optional)

I'm using ST 4085 on macOS 11 beta

[jwortmann]

Note that highlight doesn't only apply to unfocused ("other") matches from the find panel, but also when you select a full word and have multiple occurences of it in the file.

Your proposal to add highlight_background would also imply to add a highlight_foreground then, because without this it would be unlikely to find a good background color which doesn't mask the text color for all possible foreground colors from the color scheme.

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Another thing nice to have would be to add the option background with corresponding brackets_background/bracket_contents_background/tags_background colors to the available styles in brackets_options, bracket_contents_options and tags_options. By the way, bold and italic are only listed under brackets_options in the documentation, but they also work for bracket_contents_options and tags_options.