Follow-up to a Prior Conversation “A-Z Filter”

https://wordpress.org/support/topic/a-z-filter/
I see that this conversation was done over a year ago but am hoping for some advice. On @swimminghippo I went to the page reference and really like how they have their “Glossary of Trade Terms”. They have the table (which is beautifully done) and above it they have “Search” with the letters of the Alphabet and if you hover over a letter it displays a number signifying how many items will be listed. I really like that way of displaying information and would like to create something similar. I know the table is (most likely) done with TablePress but how did they create the Search with the letters of the alphabet part? Is that created with a plugin from TablePress and if yes which one?

Thank You in advance for help.
Ruth