To add an announcement bar on Squarespace, you can follow these.
#1. Click Website Tools (under Not Linked)
#2. Click Announcement Bar
#3. Click Enable Announcement Bar > Enter some text/URL then SAVE
#4. It will appear on top of the site
#5. To change the color of the Announcement Bar, you can follow this guide.
#6. To change the font of the Announcement Bar, you can follow this guide.
#7. To remove the underline under the Announcement Bar link, you can use this CSS code