Add bg+powerline background blend behavior #482

Job	Run time
test-unit-parallel (18, ubuntu)	1m 30s
test-api-parallel (18, ubuntu, chromium)	2m 29s
test-unit-parallel (18, macos)	1m 58s
lint	59s
test-api-parallel (18, ubuntu, firefox)	2m 49s
test-unit-parallel (18, windows)	6m 29s
build	1m 1s
test-playwright-parallel (18, ubuntu, chromium)	1m 32s
test-playwright-parallel (18, ubuntu, firefox)	1m 52s
test-playwright-parallel (18, ubuntu, webkit)	1m 45s
test-unit-coverage	59s
test-unit (16, ubuntu)	54s
release-dry-run (18)	1m 49s
test-unit (16, macos)	38s
test-api (18, windows, chromium)	6m 16s
test-api (18, windows, firefox)	10m 14s
test-unit (16, windows)	41s
	43m 55s

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