Adding a rainbow background to a landing page is so awesome. Please check the demo here
https://jsfiddle.net/shakalya/dmchaxfn/
Here we are setting a hue value and increasing dynamically. This is so cool where we can set the dark or light colors by setting the saturation and light property of it. Changing the Hue will the changing the color and it will be all dark shades or light shades based on the other saturation and light property. This is how its pretty cool to match the tone with the background.
HSLA
H=>Hue
S=>Saturation
L=>Light
A=>Alpha