Negative Values For Color Stops Has Interesting Effects

When I set a negative value for a color in a gradient it seems as though it reverses its flow or stop and start point. So this creates interesting effects when you have multiple colors in a radial gradient or use this with linear gradients with various degree angles . I tried setting the first color of a radial gradient to 20% then gave the second color a position value of 80% then finally I gave a third color a position of -100% making the color flow backwards which created a sharp change between the second and third colors instead of a smooth gradient. I also made a cool slash effect between two different gradients with the line of css below:

background-image: linear-gradient(35deg, #6633ff 0%, #3366ff 50%, #0099ff -100%);

I know I'm probably only scratching at the surface but thought this was cool. I wondered if you could make glossy looking buttons by giving them a sharp shadow or reflection line through the middle using this technique with linear gradients and adjusting the opacity?