Can't map a key to control+shift

[HazemHussien1]

I need to remap the letter a to type a when tapped and map it to CTRL+ SHIFT when held, i tried these solutions and none worked

leftcontrol = leftcontrol
leftshift = leftshift
control = control
shift = shift

# first try
a = overload(C-S, a)

# second try
a = overload(control+shift, a)

none of these work, please keep in mind that i mapped control to capslock later in the file as well (not sure if that makes a difference so here's my config

[ids]

*

[main]

# Maps capslock to escape when pressed and control when held.
capslock = overload(control, esc)
; = overload(control, ;)

leftcontrol = leftcontrol
leftshift = leftshift
control = control
shift = shift
compose = down

rightalt = rightalt
rightalt = overload(alt, left)

rightshift = rightshift
rightshift = overload(shift, up)

rightcontrol = rightcontrol
rightcontrol = overload(control, right)

leftcontrol = leftcontrol
leftcontrol = capslock

[nsbgn]

Try defining a custom layer with the associated modifiers:

[main]
a = overload(controlshift, a)

[controlshift:C-S]

(That said, you will probably find you'll need something like a = lettermod(controlshift, a, 50, 100) or one of the other overload variants to avoid misfires)