You can change the theme to a "Dark" mode that might be easier on the eyes. There is also a "High contrast" mode available.

 - From Teams, select the three dots next to your profile avatar in the upper banner

 - Select Settings (gear icon)

 - At the top, under General is the Theme options. Default is already selected. You can switch to Dark or High contrast. 

 - The changes take effect immediately and auto-save