This block uses SVG's linearGradient element to create a linear gradient that you can update.
Use the color picker to change the colors. Drag the circles to change the gradient's orientation.
Libraries used: D3, jQuery, Spectrum, Font Awesome
https://d3js.org/d3.v4.min.js
https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js
https://cdnjs.cloudflare.com/ajax/libs/spectrum/1.8.0/spectrum.min.js