The task was to build a cylinder and a sphere with 100% opacity. The difficulty was that there was no ready-made cylinder.

It was necessary to understand that the cylinder consists of an ellipse and a rectangle. Then combine the figures, make a linear gradient. The background is also with 100% opacity.

The line that goes onto the cylinder creates the impression that the cylinder is transparent, but this is not so. A duplicate of the line with a linear gradient of transparency goes onto the cylinder.

Radial colour gradient is used on the sphere.