Linear gradients are easy to create in CSS and are extremely useful. As we'll go through in this article, we can make them visually much smoother by creating them with non-linear gradients. Well, non-linear in the easing sense, anyway!
In Material Design style guidelines for images, the designers at Google talk about text protection gradients. They call them a scrim. They recommend:
[the] gradient should be long… with the center point about 3/10 towards the darker side of the gradient. This gives the gradient a natural falloff and avoids a sharp edge.
We can't create exactly that with linear gradients, but we can (and will) create a "low poly" approximation with more color stops.
Using only 5 color stops (like in the illustration above) would create some serious banding. Adding more stops makes the gradient a lot smoother. This is exactly what I've done in the demo you saw in the first image in this article. Il buono has a 13 color-stop gradient, which makes it blend nicer into the image.
(See the comments in the source link for Sass mixins.)