The original iPhone featured a physical Ring/Silent switch on the left side, and it has carried over to every iPhone since.

On-Off switch circuit symbol. SPST switches can also work as "push-to-make" on, where when the button is released it returns to its normally open (off) position or vice-versa. Double pole single throw ...

It's also nearly impossible to tell whether a push button is on or off, unlike modern-day light switches that can indicate by position or labels whether they're on or off. If there's faulty wiring ...

When Outlook is using the dark theme, you can switch dark mode on and off for the current message using the dark mode toggle button. Click the Switch Background button at the top of the message ...