How to prevent background from peeking through video

Question

After the video has faded in.

The gradient background peeks through the bottom at times.

You can see the tiny piece sticking out at the bottom.

So, I was thinking of trying to fade it out or do it a different way where the background becomes invincible.

Would I be able to do something like that? https://jsfiddle.net/0vw426L3/

.curtain {
  flex: 1 0 0;
  margin: auto;
  max-width: 640px;
  position: relative;
  overflow: hidden;
  background: linear-gradient(120deg, #155799, #159957);
}