Using the Module Setting Design Options
The module's settings include options for styling the button's active state. You can find these at:
Show / Hide Button Settings > Design > Active Button
Like so:

Using CSS
When the show / hide button module is active, the ".dshb-active-button" gets added to the module's outer element. That means you can use CSS to style the button like so:
body #page-container .et_pb_section div.et_pb_db_show_hide_button.dshb-active-button a.et_pb_button {
color: red !important;
}
Hello ! Love this feature, however is it possible to make one of the buttons already active on loading ?
Thanks :)
Hey Adrien, you should be able to do it by setting "Show / Hide Button Settings > Advanced > CSS ID & Classes > CSS Class" to "dshb-active-button". The module basically uses this class to track whether a button is active or not, so manually setting the class should make it treat the button as active initially.
I hope that helps, but let me know if it doesn't do what you need. Thanks!
It works perfectly thank you Dan !
Great! Thanks for letting me know, Adrien :)