Here is the CSS I use for a vertical gradient:
.calendar table:after {
content: '';
position: absolute;
top: 0;
left: 0;
right: 0;
bottom: 0;
background: linear-gradient(to bottom, rgba(0,0,0,0) 50%, rgba(0,0,0,0.48) 100%);
}
You could modify the above (using the deg angle) to create a horizontal gradient.
https://developer.mozilla.org/en-US/docs/Web/CSS/linear-gradient