1) When you include text, choose HTML under Add new block.
★ IMPORTANT ★
When you copy and paste text from a Microsoft Word file or any other platform, DO NOT paste it. Choose Paste and Match Style.
This is because a number of unnecessary code (for fonts and styles) will be copied and make the source page messy.

2) Once you were able to paste only text, you can choose styles (e.g., font size, colour, etc).

Enter Text for Class at the bottom of the block.