This way, the test log can show the expected and actual result if it fails.
thread 'steps::tests::test_conversion_fallback_colors' (61338) panicked at cosmic-theme/src/steps.rs:213:9:
assertion `left == right` failed
left: 102
right: 103
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
In Figma, themes with background lightness above 88 have their surfaces
darkened; whereas below 88 have their surfaces lightened. This fixes custom
light theme surfaces being unusually dark against a darker background.
