JSFiddle - React, Tailwind, and code Playground

HTML

<span id="wsite-nav-cart-num">99</span>

CSS

/* desk boxes*/
.desk_box_ver{ 
	width: 18px;
	height: 33px;
  margin:10px;
}	

.desk_box_ver:hover{
	cursor: pointer;
}


.desk_box_hor{ 
	width: 23px;
	height: 10px;
}	
.desk_box_hor:hover{
	cursor: pointer;
}

#wsite-nav-cart-num { 
color: #fff !important;
    margin: 0px -2px 0px -3px;
    font-family: 'futura lt' !important;
    font-size: 10.5px;
    font-weight: normal;
    letter-spacing: .2px;
    width: auto;
    text-indent: 0px;
    line-height: 10px;
    padding: 3px 5px 3px 5px !important;
    top: 5px;
    border-radius: 100%;
    z-index: 99999999999;
    height: auto;
    right: 10px;
    text-align: center;
    }

JavaScript

function colorCode(num, opts) {
	var color = [];

	if(num <= opts.start.number)
		color = opts.start.color;
	else if(num >= opts.end.number)
		color = opts.end.color;
	else {
		for(var i = 0; i < 3; i++) {
			color[i] = Math.round( (num - opts.start.number) / (opts.end.number - opts.start.number) * (opts.end.color[i] - opts.start.color[i]) + opts.start.color[i] );
		}
	}

	return 'rgb(' + color.join() + ')';
}


$('span#wsite-nav-cart-num').each(function() {
    $(this).css('background-color', colorCode(+$(this).text(), {
        start: {number: 0, color: [171,171,171]},
        end: {number: 1, color: [200,181,0]}
    }));
});