Accessibility for dark mode users

Looking for some advice. 

I created a course that uses text input boxes for the learner to use as part of a reflection exercise. 

One of the learners made me aware that they use dark mode on their laptop and they had to highlight the page in order to see anything, I have added a snippet of their explanation below.

' The training content was great but on the questions section that was requiring me to fill my answers out, I had to type and then highlight what I had typed to see that I had correctly spelt everything.'

Just wondering is anyone can advice on how to ensure they don't encounter this problem again? 

I have attached an example of one of the slides they had issue with.