Дмитрий

var acc = document.getElementsByClassName("event-accordion-item");
var i;
 
for (i = 0; i < acc.length; i++) {

  acc[i].addEventListener("click", function() {

    this.classList.toggle("active");
    var fas = this.querySelector('.eventAccordion-icon');
    if(fas.classList.contains("fa-plus-circle")){
      fas.classList.remove("fa-plus-circle");
    }
    else{
      fas.classList.add("fa-plus-circle");
    }
        fas.classList.toggle("fa-minus-circle");
    
    var panel = this.nextElementSibling;

    if (panel.style.maxHeight){
      panel.style.maxHeight = null;
       panel.style = 'margin-top: 0px; margin-bottom: 0px';
    } else {
       panel.style = 'margin-top: 25px; margin-bottom: 25px';
      panel.style.maxHeight = panel.scrollHeight + "px";

    } 
  });
}