Hi Janani,
I #2, is this a custom stylesheet? Has your developer enqueued this? If not, he’s just adding it manually which isn’t optimal because it won’t be read by optimization plugins. If it’s just a little CSS, it might be okay though.
For Step #2:
1. Go to Appearance > Elements.
2. Create a Hook Element.
3. Hook it to wp_head.
4. Add the code.
5. Set the display rule location to your preference. For instance, entire site.
For Step #3:
1. Go to Appearance > Elements.
2. Create another Hook Element.
3. Hook it to wp_footer.
4. Add the code.
5. Set the display rules as well.
Reference: https://docs.generatepress.com/article/hooks-element-overview/