New css parameter

Please tell me how to install a separate parameter css for chat button?

I want to change the font, text size and color.

Turn off CSS/JavaScript cache and compression under Admin Panel => Tools => Cache => Settings. Then use your browser's developer tools and inspect the area. You should then see CSS values that apply to the highlighted section of code. Play around until you find where the CSS is and what changes to make.

 Thanks for the answer, but the text on the button inherits the setting from the body (.bx-def-font, .bx-def-font-inputs). The change leads to a change in the text of almost all background font on the website, that's why I need a new stand-alone css parameter for this button.

 I found a solution, you must add a parameter to the first record /modules/boonex/simple_messenger/templates/base/css/simple_messenger.sss.

for example:

font-family: Roboto, Noto, Open Sans, Helvetica Neue, Helvetica, sans-serif;

Color: # 333333