Unable to see text after selecting it

You must to change a css selector called ::selection in your CSS file of your theme.

For more detail look at the links bellow:

• https://www.fwait.com/how-to-change-selected-text-background-color-in-css/
• https://www.w3schools.com/howto/howto_css_text_selection.asp

Do I need to have access to “additional CSS” for that? I don’t have a premium account.

I’m not sure.

Sorry, but now I realized that your installation’s a wordpress.com’s service. What’s a totally different service.

The better and right place for you to ask some support about your issue is directly in link bellow:

https://wordpress.com/support/contact/

This is their official support page.

Oops, sorry about that. I honestly didn’t know the difference. Thanks so much for the help.