A well-kept secret is that the <style> element can be included inside the <body> of a document. Ref. MDN web docs
For the vast majority of teachers who do not have access to the administration of their Moodle site, it can be very useful to add css on a page using the <style> tag. This can be easily be done using the 'Plain text area' editor.
However, the Atto HTML editor automatically deletes any <style> tags, apparently for no reason, making their use unnecessarily awkward. You can only edit the <style> tag in the Plain text area editor, not in the Atto editor and if you do, your css is erased!
Please modify the Atto editor so that it preserves the <style> tags.