Layout issues on landscape iPhone 11 Pro

[oolivero45]

When using an iPhone 11 Pro in landscape orientation, white pillars appear on the left and right sides of the screen, as shown in this screenshot: https://prnt.sc/qwwial.

Reproducibility

• CR on iPhone 11 Pro, iOS 13.3.1 Developer Beta (17D5004a), Firefox 21.0 (16918)
• CR on iPhone 11 Pro, iOS 13.3.1 Developer Beta (17D5004a), Chrome 79.0.3945.73
• CR on iPhone 11 Pro, iOS 13.3.1 Developer Beta (17D5004a), Safari 13