When viewing monthly calendar view (especially in dark mode) the current day (today) has only a single line highlight around the day number, this is hard to locate. Drawing a distinctive (e.g. bright yellow or orange) highlight around the whole day box or changing the background color to something contrasting would help.

All dark mode background highlights need to be 'turned up' in brightness as they are hard to see or interfere with readability. You can make these things options next to the Dark / Light / System selection to vary contrast or highlight intensity.

Thanks, loving Proton!