math inside jQuery

[Techicolors]

just to warn, i am new to programming

 

anyway, i've been trying to implement a function that when it hovers over a div cell, the shade color darkens. eventually reaching a ceiling that makes it totally dark

 

said function

$('#Shade').on('click', function() {
	$('.cell').hover(function() {
		let dark = 90;
		$('this').css('background-color', 'hsl(0, 0%, ${dark -= 10}%');
		});
});

but it doesn't work. 

 

here's the rest of the code - just FYI it's pretty much a sketchboard 

https://codepen.io/tech125/pen/zPwaoM