Start css animation in div only after opening menu

@import url('https://fonts.googleapis.com/css?family=Open+Sans:400,600,700');


body {
  margin: 0 auto;
  font-family: Open Sans;
  background: #f4f4f4;
}

.menu-container {
    width:100%;
    margin: 0 auto;
}
.menu {
    width: 100%;
    font-weight: 600;
    font-size: 14px;
    line-height: 15px;
    position: relative;
    padding: 0px 0 0px 0px;
    margin: -5px;
    background-color: #fff;
}

.logo {
  width: 40px;
  margin: 15px 1px -10px 35px;
}

.menu a, .menu a:link, .menu a:visited, .menu a:focus, span {
    color: #000000;
    font-weight: bold;
    text-decoration: none;
}
.menu a:hover {
    color: #227087;
    text-decoration: none;
}
.menu > li {
   width: 20%;
    display: inline-block;
    text-align: center;
    margin-left: -4px;
}
.menu > li > a {
    padding:20px 18px;
    display: block;
}
.menu > li:hover > a {
    color: #227087;
}
.menu > li:hover {
    background-color: #fff;
}
/* Megadrop width dropdown */
 .menu > li > .megadrop {
    opacity: 1;
    visibility: hidden; /* hidden*/
    position: absolute;
    list-style: none;
    top: 55px;
    left: 0px;
    width: 100%;
    min-height: 200px;
    text-align: left;
    margin-top:30px;
    padding: 0;
    z-index: 99;
    overflow: hidden;
   background: #212226;
    animation-duration: .15s;

    animation-name: bounceInDown;
}
.menu > li:hover .megadrop {
    opacity: 1;
    visibility: visible;
    margin-top: 0px;

}
.menu ul li:hover:after {
    color: #227087;
}
.menu .col {
    width: 14.1%;
    float: left;
    color:white;
    margin: 0 0 0 2.2%;
}
.menu .col ul {
    padding: 0;
    margin: 0;
}
.menu .col ul li {
    padding: 0;
    list-style: none;
    font-size: 15px;
}
.menu .col h3 {
    font-size: 16px;
    padding: 10px 0;
    font-weight: bold;
    margin: 5px 0 5px 0;
    color: #fff;
}
.menu .col ul li a {
    display: block;
    padding: 0 0 15px 0;
    color: #9b9b9b;
}
.menu .col ul li a:hover {
    color: #111;
}
.menu > li > ul li ul, .menu li >ul li, .menu > li > .megadrop, .menu > li > ul, .menu > li {
    transition: all 0.2s ease-in-out;
    -moz-transition: all 0.2s ease-in-out;
    -webkit-transition: all 0.2s ease-in-out;
    -ms-transition: all 0.2s ease-in-out;
    -o-transition: all 0.2s ease-in-outs;
  

}

.nav-information {
  width: 100%;
  height: 80px;
  background: #000; /*url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/62476/logo2.png) no-repeat;*/
  background-position: 2.5% 50%;
  background-size: 300px;
  display: inline-block;
}

.nav-information h3 {
  color: #fff;
  padding-left: 110px;
  line-height: 40px;
  font-weight: 400;
}

.nav-button {
  width: 80px;
  height: 80px;
  background: #6244b6 url(https://s3-us-west-2.amazonaws.com/s.cdpn.io/62476/search-icon.svg) no-repeat;
  background-size: 40%;
  background-position: 50% 50%;
  float: right;
  display: inline-block;
  margin-top: -77px;
}

.product {
  width: 200px;
  height: auto;
   -webkit-animation: NAME-YOUR-ANIMATION 6000ms;
   animation-timing-function: cubic-bezier(.69,.18,.02,.79);
 
}

@-webkit-keyframes NAME-YOUR-ANIMATION {
  0%   { opacity: 0; margin-top: -35px; }
  100% { opacity: 1; margin-top: 0px;}
}

.product img {
  width: 120px;
}

.btn-product {
  width: 120px;
  height: 30px;
  line-height: 30px;
  margin-top: 5px;
  margin-bottom: 10px;
  float: left;
  background: #fff;
  color: #212226;
  border-radius: 50px;
  display:block;
  text-align: center;
  transition: 200ms;
    box-shadow: 0 0 3px blue;

}

.btn-product:hover {
  color: #fff;
  background: #000;
}

.btn-product:active,:focus {
  border-radius: 50px;
  box-shadow: 0 0 3px #000ac3;
}

<div class="nav-information">
  <h3></h3>
  <div class="nav-button"></div>
</div>

<ul class="menu">
  <li>
    <a href="#">+JOGOS</a>

          
        </li>
        <li class="dropdown"> <a href="#">FAQ</a>

          
        </li>
        <li class="dropdown"><a href="#">+ABRIR MENU</a>

            <div class="megadrop">
                <div class="col">
                     <h3>MAIS RECENTES</h3>

                    <ul>
                        <li><a href="#">Grand Theft Auto V</a>
                        </li>
                        <li><a href="#">Battlefield 1</a>
                        </li>
                        <li><a href="#">Destiny 2</a>
                        </li>
                       <li><a href="#">Far Cry 5</a>
                        </li>
                        <li><a href="#">The Crew 2</a>
                        </li>
                    </ul>
                </div>
                <div class="col">
                  <h3>DESTAQUE</h3>
                    <div class="product">
                      <img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/62476/gtav_ps4_.png"><aclass="btn-product" href="#">COMPRAR</a>
                  </div>
<div class="product">
                      <img src="https://s3-us-west-2.amazonaws.com/s.cdpn.io/62476/need%20for%20speed%202016%20cover.png"><aclass="btn-product" href="#">COMPRAR</a>
                  </div>
                    
                </div>
                <div class="col">
                     <h3>Title</h3>

                    <ul>
                        <li><a href="#">Sub-menu 1</a>
                        </li>
                        <li><a href="#">Sub-menu 2</a>
                        </li>
                        <li><a href="#">Sub-menu 3</a>
                        </li>
                    </ul>
                </div>
                <div class="col">
                     <h3>Title</h3>

                    <ul>
                        <li><a href="#">Sub-menu 1</a>
                        </li>
                        <li><a href="#">Sub-menu 2</a>
                        </li>
                        <li><a href="#">Sub-menu 3</a>
                        </li>
                    </ul>
                </div>
            </div>
        </li>
        <li><a href="#">SOBRE</a>
        </li>
        <li><a href="#">CONTATO</a>
        </li>
        </li>
    </ul>
</div>