There is an option to adjust the colors for the shortcodes.
We resize images in shortcodes to improve loading speed. But if you intend to change the size in shortcodes you can follow the link below: https://webnus.net/dox/modern-events-calendar/image-size-in-shortcodes
You can change the size for desktop and mobile here: MEC Settings > Styling.
You can activate Dark Mode in MEC by going to: MEC Settings > Styling.
Let me know if you have any other questions in the comment area.