I am a newbie with Fortuna theme (yet I am seasonal web developer) and found it confusing to find my way as of how to customize things around.
In general: I am lacking “API refference” documentation, e.g. to know all the attributes of the Fortuna tags.

In particular I want to change the color of accordion toggle (+/-) switch, as the reddish color of my theme makes it look like “stop sign”

Thanks

The best way would be to use the Dev tools console and see the actual classes of the elements.
For example for the accordion you can add this CSS:

.acc_control {
    background-color: green !important;
}