fix zoom slider color problem in dark mode

It looks more like a defect but support insists it's by design.

The selected part in zoom slider is hard to distinguish from the total slider in dark mode, due to the color of them is almost identical, see attached screenshot.

It would be much easier to read for example if the color of the selectecd part is the same as in filter panel, e.g. blue.

It's quite easy to embed a text area and using a few line of JavaScript code to change this color, but it's quite difficult for end users to utilize this, aka, they have to put this text area and JavaScript code in all of their reports and pages.

$('div.sf-element-zoom-slider div.sf-element-range.sfc-inner.TouchTarget').css({
"background-color": "#7289F9"
});