Just like to share stuff and so much I have learned, has come from people sharing too!
You have to add the CSS centrally to your site and to do this you need to be Admin, have admin permissions or to be very good friends with the Admin :O) This can be challenging as CSS is applied across all areas linked to the Admin! (maybe there is a way to have sub-level styles and themes but don't think our own set up allows this).
Fortunately, in my role, I am also the Admin to our Canvas instance so I have access to the Themes are and can upload a CSS file. I don't have any particular programming skills just some interest, curiosity and a willingness to try things out.
I experiment a bit on our beta instance to see what I can alter. Most of the css changes are cosmetic but have helped personalise our instance and some of the stuff I have outlined here - A bit of Modding of the Module - Playing about wi... - Instructure Community - 588090 (canvaslms.com...
The flip feature I just added from the W3C site I mentioned in the post but made a few minor modifications.
On the actual Canvas page, to get the boxes to line up, I found some <div> coding on the Community for creating tables:
<div class="content-box">
<div class="grid-row">
<div class="col-xs-12 col-md-4" style="padding: 0;">
See - Use Divs Instead of Tables on Home Page - Instructure Community - 209087 (canvaslms.com) for more details
I also adapted some great ideas for page borders from Lauren's (Canvas Queen) YouTube site - Create a Canvas Home Page Quickly with Canva (youtube.com)
I've added a brief video of how the page views and works above...