How to properly make a triangle pseudo-element in a menu? [closed]

.row {
  padding: 0;
}

.container-fluid {
  padding: 0;
  margin: 0;
}

.top-nav_btn {
  display: none;
  width: 20px;
  height: 20px;
  background-color: transparent;
  border: none;
  font-size: 18px;
  position: absolute;
  right: 30px;
  top: -80px;
}

.top-nav_btn ::hover {
  cursor: pointer;
}

.top-nav {
  background-image: url(../img/background/header-1440.svg);
  position: relative;
  background-size: 100%;
  height: 104px;
  background-repeat: no-repeat;
}

.logo-header_green {
  position: relative;
  margin: 21px;
  width: 75px;
  height: 75px;
}

.logo-footer_white {
  width: 75px;
  height: 75px;
}

.top-nav_menu {
  list-style: none;
  margin: 0;
  padding: 31px 11px;
  display: flex;
  align-items: center;
  position: relative;
}

.top-nav_menu a {
  color: var(--active-text-color);
}

.top-nav_menu li {
  margin-right: 45px;
}

.top-nav_menu li a {
  text-transform: uppercase;
  text-decoration: none;
  font-weight: 700
}

.top-nav_menu li a::after {
  content: '';
  width: 100%;
  height: 3px;
  background-color: var(--active-block);
  display: block;
  transform: translateY(42px) scale(0);
  transition: all 0.2s;
}

.top-nav_menu li a:hover {
  text-decoration: none;
}

.top-nav_menu li a:hover::after {
  transform: translateY(42px) scale(1);
}

.sub-menu a {
  display: block;
  padding: 16px 32px;
  color: #000;
  font-size: 15px;
  line-height: 180%;
}

.sub-menu {
  list-style: none;
  position: absolute;
  z-index: 99999;
  top: 100%;
  left: 0;
  -webkit-transition: 0.5s ease-in-out;
  -moz-transition: 0.5s ease-in-out;
  -o-transition: 0.5s ease-in-out;
  transition: 0.5s ease-in-out;
  background: #fff;
  box-shadow: 0 0 17px rgba(178, 191, 204, .25);
}

.sub-menu li a::after {
  display: none;
}

.menu-item-has-children {
  width: 0;
  border: 4px solid transparent;
  border-bottom: none;
  border-top-color: #8a8383;
  content: '';
  vertical-align: middle;
  display: inline-block;
  position: relative;
  right: 5px;
}

.top-nav_menu .sub-menu {
  display: none;
}

.top-nav_menu li:hover .sub-menu {
  display: block;
}

.top-nav_contact {
  list-style: none;
  padding: 0;
  display: flex;
}

.top-nav_contact a {
  margin-right: 45px;
  color: var(--active-text-color);
}

<div class="top-nav">
  <div class="row justify-content-between align-items-center p-0 m-0">
    <div class="col-md-6 p-0 m-0">
      <ul id="top-nav_menu" class="top-nav_menu">
        <li id="menu-item-870" class="menu-item menu-item-type-post_type menu-item-object-page current-page-ancestor current-menu-ancestor current-menu-parent current-page-parent current_page_parent current_page_ancestor menu-item-has-children menu-item-870"><a>Программы обучения</a>
          <ul class="sub-menu">
            <li id="menu-item-899" class="menu-item menu-item-type-post_type menu-item-object-page current-menu-item page_item page-item-896 current_page_item menu-item-899"><a href="" aria-current="page">Повышение квалификации</a></li>
            <li id="menu-item-900" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-900"><a href="">Переподготовка</a></li>
            <li id="menu-item-901" class="menu-item menu-item-type-post_type menu-item-object-page menu-item-901"><a href="">Подготовка</a></li>
          </ul>
        </li>
      </ul>
    </div>
  </div>
</div>