<div class="blocks">
  <div class="block"></div>
  <div class="block"></div>
  <div class="block"></div>
  <div class="block"></div>
</div>

.blocks {
  width: 100%;
  display: flex;
  justify-content: space-around;
}

.block {
  background-color: blue;
  width: 200px;
  height: 200px;
  transition: 0.4s;
}

.block_red {
  background-color: red;
}

.block_blured {
  background-color: green;
}

$(".block").mouseenter(function() {
  $(".block").removeClass("block_red")
  $(".block").addClass("block_blured")
  $(this).removeClass("block_blured")
  $(this).addClass("block_red")
})