How to colour Sundays in awesome-wm calendar?

Question

I have the following code for a calendar which I attach to a date text e.g. 15 Jan 2024:

mytextcalendar = wibox.widget.textclock("%d %b %Y", 2, "Europe/London")

local function rounded_shape(size, partial)
    if partial then
        return function(cr, width, height)
                   gears.shape.partially_rounded_rect(cr, width, height,
                        false, true, false, true, 5)
               end
    else
        return function(cr, width, height)
                   gears.shape.rounded_rect(cr, width, height, size)
               end
    end
end

local month_calendar = awful.widget.calendar_popup.year({
                 font = "monaco 11", 
                 opacity=0.8,
                 spacing=0,
                 margin=0,
                 style_month   = { padding      = 0,
                                   bg_color     = '#222222',
                                   border_width = 3,
                                   border_color = '#222222',
                                   shape        = rounded_shape(10)},
                 style_normal  = { shape    = rounded_shape(5), },
                 style_focus   = { fg_color = '#222222',
                                   bg_color = '#ff9800',
                                   shape    = rounded_shape(5, true)},
                 style_header  = { fg_color = '#ff9800',
                                   border_width = 0,
                                   shape    = rounded_shape(10)},
                                   
                 style_yearheader = {border_width = 0,
                                     bg_color = '#222222',
                                     fg_color = '#ff9800'},
                                     
                 style_weekday = { fg_color = '#de5e1e',
                                   border_width = 0,
                                   shape    = rounded_shape(5)}
                 })
month_calendar:attach( mytextcalendar, "tr", { on_hover = false, })

Then I simply add the variable mytextcalendar to the systemtray, which works okay.

---

What I would like to do is to change the background of Saturdays and Sundays. I already found it done here

The only problem is that I can't find a way to transfer the code over. Mainly my question is: how can I use fn_embed = decorate_cell, (which is in the documentation) with my code?