I recently wrote this line of CSS inside of a .less file....

background: linear-gradient(#fff0, #fff);

...after first trying it out inside the browser inspector, where it worked as expected, rendering a gradient background from transparent fading into white.

However, it did not work correctly after compiling the LESS file. It looks like it was getting compiled to:

background: linear-gradient(#ffffff 0, #ffffff);

Even writing #ffffff00 would cause LESS to compile it to the less helpful #ffffff 0, which is... interesting. I ended up having to use rgba() as a workaround.

background: linear-gradient(rgba(0,0,0,0), #fff); 

That worked.