The tutorial doesn't have a high contrast with the background

[Helen09]

Repro steps: • Navigate to https://makecode.adafruit.com/beta • Click "Siren" under Tutorials and click "Start Tutorial" to open open this tutorial • Click "Next" to look the tutorial

Expected result:(Micro:bit) The tutorial should have a high contrast with the background

Actual result:(Adafruit) The tutorial doesn't have a high contrast with the background