Seeing white hairlines on the sides of my full width video on my actual phone.

Site: https://leopard-heptagon-k5fx.squarespace.com/
PW: horses

Hi there, so this top full bleed video has been giving me a lot of issues (mainly giving me too much white space underneath the video), but its finally close to something i can live with, thanks to Custom CSS i found on this forum.

however, now when i preview it on my actual iPhone browser (Safari and chrome), I am seeing a white hairline on the left and right edges of the video/browser (screenshot attached).

When the site initially loads, it looks fine for a split second, and then the hairline seems to come in, so i am assuming its the CSS code?

any help is appreciated!