Support a better high contrast mode for Blockly blocks (#3718)
Support a better high contrast mode for Blockly blocks (#3718)


switchinnovations/pxt,switchinnovations/pxt,Microsoft/pxt,Microsoft/pxt,switch-education/pxt,switch-education/pxt,playi/pxt,switch-education/pxt,switchinnovations/pxt,playi/pxt,Microsoft/pxt,playi/pxt,Microsoft/pxt,switchinnovations/pxt,playi/pxt,Microsoft/pxt,switch-education/pxt,switch-education/pxt