* {
  box-sizing: border-box;
}

body {
  background-color: bisque;
  height: 100vh;
  margin: 0;
  display: flex;
  align-items: center; /*cross axis here column so horizontal*/
  justify-content: center; /*main axis here column so vertical*/
}

.empty {
  height: 150px;
  width: 150px;
  background-color: #fff;
  margin: 20px;
  border: 1px solid black;
}

.fill {
  background-image: url('https://source.unsplash.com/random/100x100');
  width: 148px;
  height: 148px;
  cursor: pointer;
}

.hold {
  border: 2px solid black;
}

.hovered {
  background-color: #333;
  border-color: #fff;
  border-style: dashed;
  border-width: 2px;
}

@media (max-width: 800px) {
  body {
    flex-direction: column;
  }
}