Which statement describes how a stacking context is created?

Which statement describes how a stacking context is created?

• A. Positioning alone creates a stacking context.
• B. A stacking context is created by transform.
• C. A stacking context is created by properties like position, opacity, and transform.
• D. Z-index on a static element creates a stacking context.

Answer: (C)

Stacking contexts form whenever an element’s CSS properties establish a new local stacking order. This isn’t caused by positioning alone; you typically need a positioned element with a z-index value, or other properties like opacity less than 1 or a transform to trigger one. Transform creates its own stacking context, and opacity below 1 does so as well, even if other layout properties don’t change. Because the strongest, most accurate description is that a stacking context can be created by a combination of properties—position, opacity, and transform—the statement that mentions these properties together is the best fit. The other ideas are incomplete: positioning alone isn’t always enough; z-index on a static element doesn’t create a stacking context; and transform is a valid trigger but not the only one.

Stacking contexts form whenever an element’s CSS properties establish a new local stacking order. This isn’t caused by positioning alone; you typically need a positioned element with a z-index value, or other properties like opacity less than 1 or a transform to trigger one. Transform creates its own stacking context, and opacity below 1 does so as well, even if other layout properties don’t change. Because the strongest, most accurate description is that a stacking context can be created by a combination of properties—position, opacity, and transform—the statement that mentions these properties together is the best fit. The other ideas are incomplete: positioning alone isn’t always enough; z-index on a static element doesn’t create a stacking context; and transform is a valid trigger but not the only one.