How to code an idle game?

I got an idea for an idle game, but I have no idea where to start coding it. I already do Python and I know the basic of HTML/CSS, being familiar with the python Django framework, but I don't think any of those would do it by themselves.

The idea is for a browser game in Absorber style (or cookie clicker for a more general reference). Where do I start? What language/tools do I use?