The black and white XYZ tile used in the video is apparently discontinued.
Try ESRI WorldGreyCanvas (this URL goes in the field in QGIS - clicking it won't work)
server.arcgisonline.com/ArcGI...{z}/{y}/{x}
Or find an appropriate one here:
wiki.openstreetmap.org/wiki/T...
Something not working for you? Try the following suggested by one of my amazing students:
1. Check in your data attributes table whether you've definitely put the right code from the JNCC handbook - an easy mistake to make.
2. When you've applied the symbology, make sure when you categorise the data and select P1codes with the little abc next to it as this is the part with the correct data in. QGIS offered me an empty data set named P1codes the first time I tried this, and I had to switch to the field I had created.
3. Make sure the style file applied is for polygons, not accidentally for lines.