on_highlights does not allow me to change the comment collor

[joviol]

Hello,

I am trying to change the Comment's color to a slightly brighter shade. I though that using the following code would help:
on_highlights = function(hl)
hl.Comment = { fg = , style = { italic = true }}
end,

however it does no work.
I ended up adding the following code at the end of my config file:
vim.api.nvim_set_hl(0, 'Comment', { fg = '#767cb9', italic = true })

but it feels that the on_highlights function should have done the trick
I am aslo having trouble controling what is italic and what is not:
With the following config:
styles = {
-- Style to be applied to different syntax groups
-- Value is any valid attr-list value for :help nvim_set_hl
functions = { italic = true },
keywords = { italic = true },
string = { italic = true },
variables = { italic = true },
-- Background styles. Can be "dark", "transparent" or "normal"
sidebars = 'dark', -- style for sidebars, see below
floats = 'dark', -- style for floating windows
},

I would expect function names for example to be italic
however the only thing that is displayed as italic are a few keywords (const, return, export) not all of them
I was wondering if there is something I am missing in my config?

[joviol]

Sorry there was a mistake in my configuration