A small thing this but, at some point, the Power BI default theme was changed to an eyesore of a palette reminiscent of the awful highlighting sometimes used in Excel by finance teams. Aside from being a bit ugly I’ve used the previous default theme for all my historical reports and want to keep this style. The old default is still available as the Classic theme.
Under the Home ribbon in Power BI Desktop you can find the Classic them hidden away under Switch Theme – More Themes: