Add bg+powerline background blend behavior #484

Job	Run time
lint	54s
build	56s
test-api-parallel (18, ubuntu, chromium)	2m 24s
test-api-parallel (18, ubuntu, firefox)	2m 41s
test-unit-parallel (18, ubuntu)	1m 26s
test-playwright-parallel (18, ubuntu, chromium)	1m 28s
test-unit-parallel (18, macos)	1m 35s
test-unit-parallel (18, windows)	4m 18s
test-playwright-parallel (18, ubuntu, firefox)	1m 33s
test-playwright-parallel (18, ubuntu, webkit)	1m 30s
release-dry-run (18)	1m 45s
test-unit-coverage	58s
test-api (18, windows, chromium)	6m 46s
test-unit (16, ubuntu)	42s
test-api (18, windows, firefox)	5m 25s
test-unit (16, macos)	28s
test-unit (16, windows)	31s
	35m 20s

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