Draft: fix #24

[Dufgui]

Describe your changes

Fix #24

Issue ticket number and link

#24

Checklist before requesting a review

• I have read and understand the Contributions section
• I have performed a self-review of my code
• I ran the unit tests and my PR does not break any tests
• I documented the changes I've made on the CHANGES.md and followed actual conventions
• I added a new section on how-to.md (optional)

[dufoli]

button is alrady added through dom so too late to add event handler.
Best is to use addEventListener

[dufoli]

div element must be draggable:
https://developer.mozilla.org/en-US/docs/Web/API/HTMLElement/dragstart_event

Anyway, best is to catch mousedown and mouseup because dragable will add next to pointer the element whereas we need to update position of button.
mousedown => store the initial mouse X and mouseY and initial button position + add listener on mousemove
mousemove => calculate diff between current position and mouse original position and add delta only on Y to button position (btnYPos = btnYOriginPos + deltaY)
mouseup: remove listener mousmove

[dufoli]

I have fixd major issue but I found that still bugy with some weird behaviour.

[dufoli]

I will squash and merge.