body{
  font-family: Roboto;
  background-color: #000;
}

#header_block{
  text-align: center;
}

#grid_container{
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

.post_box{
  width: 321px;
  height: 209px;
  background-color: #ddd;
  margin: 12px;
  position: relative;
  cursor: pointer;
}

.tile_title{
  position: absolute;
  bottom: 8px;
  left: 0px;
  text-align: center;
  background-color: #FFFFFFBB;
  width: 100%;
  font-size: 21px;
}

.post_box img:hover~.tile_desc{
  display: block;
}

.tile_desc{
  position: absolute;
  top: 21px;
  left: 0px;
  text-align: center;
  background-color: #FFFFFFDD;
  width: 100%;
  font-size: 18px;
  display: none;
}

.post_box img{
  width: 321px;
  height: 209px;
}