func setupSlider() {
// The color is supposed to be the same color as slider's backgroundColor or superview color.
slider.thumbOuterColor = .white // Set the color of the thumb outer side. 

slider.setMinimumTrackTintColor(.darkGray, for: .normal) 
slider.setMinimumTrackTintColor(primaryColor, for: .highlighted)
slider.maximumTrackTintColor = .lightGray 
slider.setCircleThumb(color: .darkGray, for: .normal) 
slider.setCircleThumb(color: primaryColor, for: .highlighted)
}