What is a potential performance concern with large blur box-shadows, and how can you mitigate?

• A. They increase CPU usage.
• B. Large blur shadows cause heavy painting; mitigate by reducing blur or using a gradient on a pseudo-element.
• C. They block GPU texture uploads.
• D. They disable compositing.

Answer: (B)

Large blur shadows demand heavy painting because the blur must blend a lot of pixels to create the soft edge, which can slow rendering, especially on less powerful devices. A practical way to mitigate this is to reduce the blur radius, cutting down the amount of work the browser does to generate the soft edge. Alternatively, use a gradient on a pseudo-element behind the element to simulate the shadow; this often paints more efficiently while still achieving a soft, spread-out look. The other options—CPU usage, blocking GPU texture uploads, or disabling compositing—don’t typically describe the common performance cost of a large blur shadow.