I am looking for a freely placeble/configurable button type...

Hello @all,
my name is Heinz and i am the new one...i am a complete newbie to Drupal (I am using Drupal 8 for things).
I have programming experience with c/c++ for some years and i started with PHP a while ago.
My problem is that i need a button-element which is configurable:
-Size(The caption will be of various length and width)
-Color(At least the background color should be adjustable)
-and it should be placeable freely in my content.
Background:
I want to add this button to the page to indicate lets say a meeting. So if a logged-in user want to attend the meeting, he would press the button and show, i want to attend the meeting. Afterwards the "button" should be published on the user-page to show that s/he attended this meeting at a given date/location(Therefore the variable caption). The background color should indicate the status of the meeting.
For the sake of simplicity i choose for this example three colors:
-GREEN: The meeting will be held as advertised.
-YELLOW: Something has changed.
-RED: The meeting has been cancelled.
So every time a user logs onto his page s/he sees the button and knows that s/he had attended the meeting.
When the user want to cancel the meeting, because the in-laws are coming s/he would simply click the button and cancel the meeting(Maybe a pop-up window/redirect to the originating page...).
On the other hand if something changed with the meeting the button should change color and the caption accordingly. By clicking the button the user would get the changed information or if canceled ... i think you get the idea...if not feel free to ask...;-)...
I searched for myself and I am bit confused because i don't know is this a core or a theme issue?
I will greatly appreciate your help and thanx in advance,
cheers HeinZ