Bluefish is an extremely powerful text based HTML editor. Actually it is more than that. It also has support for over twenty other languages including C++, D, Java, PHP, Perl, Python, Ruby...well, the list goes on. What is does is make editing easy, especially for multi-document projects like a website. To quote Wikipedia,
Bluefish fills the niche market between the plain text editors and the full IDE
To install Bluefish on KDE neon, open Konsole and type,
sudo apt install bluefish
then enter your admin password and wait for the installation to finish.
After install the program can be opened by going to the Applications Menu and either selecting it and typing Bluefish or visiting Applications/Development/Web Development.
There are a lot of really powerful tools in Bluefish but the best place to start is by creating a new file using File/New From Template in the top menu or if you have existing files you can browse to the folder they are in and open them using the file explorer on the left hand side. There is also a preview in browser button in the menu bar to make life a little more simple.
(If you are going to do some web development when there is a tutorial about installing XAMPP for web development on KDE neon here. XAMPP is a preconfigured Apache, MySQL and PHP/Perl installation to make web dev easier.)