To do it properly, you need a bit more than just `backdrop-filter: blur(8px)`; see <https://www.joshwcomeau.com/css/backdrop-filter/#the-issue-2 https://www.jos

To do it properly, you need a bit more than just `backdrop-filter: blur(8px)`; see <https://www.joshwcomeau.com/css/backdrop-filter/#the-issue-2 https://www.joshwcomeau.com/css/backdrop-filter/#the-issue-2> for a clear demonstration of the problem, and the rest of that article for the solution (with further relevant details and discussion in <https://news.ycombinator.com/item?id=42302907 https://news.ycombinator.com/item?id=42302907>; in this particular case, the backdrop blur needs to be able to access 15px more of the backdrop than it can unless you go out of your way to give it that).