How can I center a flex item both vertically and horizontally within its container?

<!-- BEGIN COPY / PASTE -->
    <div class="flex-container">
      <div class="flex-item">Centered Item</div>
    </div>

    <style>
      .flex-container {
        display: flex;
        justify-content: center; /* Centers horizontally */
        align-items: center;    /* Centers vertically */
        height: 200px;          /* Example height for vertical centering */
        border: 1px solid #ccc; /* Optional styling for visibility */
      }
      .flex-item {
        padding: 10px;
        background-color: #f0f0f0; /* Optional styling for visibility */
      }
    </style>
    <!-- END COPY / PASTE -->