<div class="flex-container">
  <div class="flex-item margin-right">margin</div>
  <div class="flex-item">item</div>
  <div class="flex-item">item</div>
  <div class="flex-item">item</div>
</div>

.flex-container {
  display: flex;
  margin-bottom: 20px;
  padding: 10px;
  background-color: #ccc;
}

.flex-item {
  margin: 10px;
  padding: 10px;
  background-color: yellow;
}

.margin-right {
  margin-right: auto;
}