When in the web view of Proton Mail, you can show the calendar by clicking the icon on the right side of the screen. The problem is, this causes the calendar to overlay all the controls on the right side of the screen. For users that'd just want their "today" view open all day, this is annoying as it prevents use of those controls. Instead of overlaying these controls (bad UX), the calendar column should just push the mail UI to the left while it is open.