Cacher is the code snippet organizer for pro developers

body {
  padding: 0;
  margin: 0;
}

.card-container {
  display: flex;
  flex-direction: row;
  justify-content: center;
  flex-wrap: wrap;
  margin: 10px;
}

.card {
  display: flex;
  flex-direction: column;
  justify-content: center;
  width: 350px;
  height: 250px;
  margin: 15px;
  border-radius: 4px;
  background: #3861c9;
}



@media (min-width: 768px) {
  .card-container {
    margin: 10px;
  }
}

@media (min-width: 900px) {
  .card-container {
    display: flex;
    flex-direction: row;
    justify-content: center;
    flex-wrap: wrap;
    margin: 15px 0;
  }
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>

 <div class="card-container">
  
    <div class="card">
      
    </div>
    
    <div class="card">
      
    </div>
    
    <div class="card">
      
    </div>
    
    <div class="card">
      
    </div>
    
    <div class="card">
      
    </div>
   
    <div class="card">
      
    </div>

  </div>