You can change your Outlook theme in your account settings while logged in through a browser or in the Mac and Windows apps.
To change the font in Outlook, head to the "Signatures and Stationery" menu, where you can pick from a number of fonts.
Microsoft pushes often for accessibility and inclusiveness, which I love. But recently, it bungled a change in the web-based version of Outlook while pursuing this goal. The first method is fastest, ...