Slider + TrackLayer

Slider.swift

private let trackLayer = CAGradientLayer() // Step 7

// Step 7
private func configureTrackLayer() {
    let firstColor = UIColor(red: 210/255, green: 152/255, blue: 238/255, alpha: 1).cgColor
    let secondColor = UIColor(red: 166/255, green: 20/255, blue: 217/255, alpha: 1).cgColor
    trackLayer.colors = [firstColor, secondColor]
    trackLayer.startPoint = .init(x: 0, y: 0.5)
    trackLayer.endPoint = .init(x: 1, y: 0.5)
    trackLayer.frame = .init(x: 0, 
                             y: frame.height / 4, 
                             width: 0, 
                             height: frame.height / 2)
    trackLayer.cornerRadius = trackLayer.frame.height / 2
    layer.insertSublayer(trackLayer, at: 1)
}