I find it a little overwhelming.

Like erikrthoff suggested, I'd drop the light mode toggle and just go with prefers-color-scheme. Then I'd move the X buttons to the top-right of their respective sections (timers, segments), and move the Add Timer button underneath.

Mockup: https://i.imgur.com/EcSHX7S.png

What a great suggestion, and you even made a mockup! That's so considerate of you, thank you so much.

I'll try to implement these UI changes tonight.