How to create a parallax scrolling effect

In Visual Composer (or equivalent):

1. Create a row
2. Add an image as background
3. Assign a custom class to the row (example: homepage-parallax-image)

Then, in Appearance > Customize > Additional CSS, paste the following:

.homepage-parallax-image {
  height: 300px; /* change value as needed */
  background-attachment: fixed;
  background-position: center;
  background-repeat: no-repeat;
  background-size: cover;
}

Source: https://www.w3schools.com/howto/howto_css_parallax.asp