$(document).ready(function() {
  let c = document.getElementsByClassName("collapsible");

  for (let i = 0; i < c.length; i++) {
    c[i].addEventListener("click", function() {
      this.classList.toggle("button-outline");
      var content = this.nextElementSibling;
      if (content.style.display === "block") {
        content.style.display = "none";
      } else {
        content.style.display = "block";
      }
    });
  }
});