Thank you for the help!

I could fix the two problems the next way:

To fix the problem with the div of 0x0 size, I changed the next property of my carousel class.

@media (max-width: 780px) {
  .container {
    grid-template-columns: 100%;
  }
}

To fix the problem with the gap, I only put the media query at the end of my styles.