Changing the background color in Rise

Rise 360: Two year and still no fix to change the entire page color to something other than white: 
The hard code css is .blocks-lesson { background: #fff; }

On a themes with black blocks the end of the page has a big ugly white section. 
.blocks-lesson { background: #000; } would fix this.
Please, have a background page color option for the entire course and/or page.

If anyone knows how to add a simple JavaScript in Rise 360, please tell.

//.blocks-lesson {  background: #000; }

const style = document.createElement("style");
style.textContent = '.pageColor { background: #000; }';
document.head.appendChild(style);

const elements = document.getElementsByClassName("blocks-lesson");

for (let i = 0; i < elements.length; i++) {
  elements[i].classList.add("pageColor");
}