add CSS Theme Selection environment variable #3922

Job	Run time
Artifact key	7s
Artifact key	8s
Foundry secrets	7s
Foundry secrets	15s
Docker secrets	10s
Docker secrets	7s
Config / Convert platforms CSV to JSON	11s
Config / Convert platforms CSV to JSON	11s
Config / Diagnostics	29s
Config / Diagnostics	29s
Metadata / Calculate variables	21s
Metadata / Calculate variables	21s
Lint / Lint sources	48s
Lint / Lint sources	48s
Build pre-installed test image	0s
Build pre-installed test image	0s
Build normal test image / Build image	1m 4s
Build normal test image / Build image	1m 4s
Test pre-installed image	0s
Test pre-installed image	0s
Test normal image	0s
Test normal image	0s
Build platform	0s
Build platform	0s
Bill of Materials	0s
Bill of Materials	0s
Publish image	0s
Publish image	0s
Publish docs	0s
Publish docs	0s
	6m 40s

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