Restructure themes.

[shadmansaleh]

Changing color for all section based on mode doesn't make sense in my opinion. Most of the themes just change section_a color for modes to change color of mode component. I think this pattern is here because of bad design of themes . I'd like to change themes to something like this

theme = {
  sections = {a={fg=, bg=, gui=}, b={}, c={}, (optional x, y, z)}, -- z defaults to a, y -> b, x -> c
  inactive = {a={}, b={}, c={},  (optional x, y, z)}, -- optional inactive status color customization defaults to sections
  tabline = {a={}, b={}, c={},  (optional x, y, z)}, -- optional tabline color customization defaults to sections
  components = { -- optional component specific color customization.
    mode = { --mode colors effecting only mode component
      normal = {},
      insert = {},
      ...
   },
   diagnostics = { -- defaults for diagnostics_color option
       error = {},
       warn = {},
       ...
    }
   ....
   -- (other components)
}

You can share what you think about the idea here.

[clason]

Will highlight group names still be supported? (I assume yes if you assign a string instead of a table to, e.g., a, but want to make sure.)

Otherwise this sounds reasonable!

[shadmansaleh]

Will highlight group names still be supported? (I assume yes if you assign a string instead of a table to, e.g., a, but want to make sure.)

Of course this won't remove any current capability from themes. Instead will give them more power (tabline & component color customization in themes) . Making sections change colors like current themes will also be possible using functions (I plan to be done with #566 by then) in new format.

[dcordb]

I think another good idea can be to put the colors table itself into the table you suggest, to be able to use this colors for custom components on lualine.