style(lemon-ui): Make `Sparkline` look great #42723

Job	Run time
Visual regression tests (chromium, 1)	6m 41s
Visual regression tests (chromium, 2)	7m 53s
Publish to Chromatic	3m 29s
Visual regression tests (webkit, 1)	3m 59s
Visual regression tests (webkit, 2)	5m 42s
Summarize visual regression tests	7s
	27m 51s

Provide feedback