In this case you only need to copy a fragment of the code and adjust the chat styles. For example:

HTML:

    <mdb-card class="chat-room small-chat wide" id="myForm">
      <mdb-card-header
        class="white d-flex justify-content-between p-2"
        id="toggle"
        style="cursor: pointer;"
      >
        <div class="heading d-flex justify-content-start">
          <div class="profile-photo">
            <img
              src="https://mdbootstrap.com/img/Photos/Avatars/avatar-6.jpg"
              alt="avatar"
              class="avatar rounded-circle mr-2 ml-0"
            />
            <span class="state"></span>
          </div>
          <div class="data">
            <p class="name mb-0"><strong>John Smith</strong></p>
            <p class="activity text-muted mb-0">Active now</p>
          </div>
        </div>
        <div class="icons grey-text">
          <a class="feature">
            <mdb-icon fas icon="video" class="mr-2"></mdb-icon>
          </a>
          <a class="feature">
            <mdb-icon fas icon="phone" class="mr-2"></mdb-icon>
          </a>
          <a class="feature">
            <mdb-icon fas icon="cog" class="mr-2"></mdb-icon>
          </a>
          <a type="button" id="closeButton">
            <mdb-icon fas icon="times" class="mr-2"></mdb-icon>
          </a>
        </div>
      </mdb-card-header>
      <div class="my-custom-scrollbar">
        <mdb-card-body class="p-3">
          <div class="chat-message">
            <div class="media mb-3">
              <img
                class="d-flex rounded mr-2"
                src="https://mdbootstrap.com/img/Photos/Avatars/avatar-6.jpg"
                alt="Generic placeholder image"
              />
              <div class="media-body">
                <p class="my-0">You're friends on Facebook</p>
                <p class="mb-0 text-muted">Web Designer at MDBootstrap</p>
                <p class="mb-0 text-muted">Lives in Paris</p>
              </div>
            </div>
            <mdb-card bgColor="bg-primary" class="rounded w-75 float-right z-depth-0 mb-1">
              <mdb-card-body class="p-2">
                <mdb-card-text class="text-white"
                  >Lorem ipsum dolor sit amet consectetur adipisicing elit voluptatem cum eum
                  tempore.
                </mdb-card-text>
              </mdb-card-body>
            </mdb-card>
            <mdb-card bgColor="bg-primary" class="rounded w-50 float-right z-depth-0 mb-2">
              <mdb-card-body class="p-2">
                <mdb-card-text class="text-white"
                  >Rem suscipit lorum repellendus ditiis?</mdb-card-text
                >
              </mdb-card-body>
            </mdb-card>
            <mdb-card bgColor="bg-light" class="rounded w-75 z-depth-0 mb-2 message-text">
              <mdb-card-body class="p-2">
                <mdb-card-text class="black-text"
                  >Nostrum minima cupiditate assumenda, atque cumque hic voluptatibus at
                  corporis maxime quam harum.
                </mdb-card-text>
              </mdb-card-body>
            </mdb-card>
            <div class="d-flex justify-content-start">
              <div class="profile-photo message-photo">
                <img
                  src="https://mdbootstrap.com/img/Photos/Avatars/avatar-6.jpg"
                  alt="avatar"
                  class="avatar rounded-circle mr-2 ml-0"
                />
                <span class="state"></span>
              </div>
              <mdb-card bgColor="bg-light" class="rounded w-75 z-depth-0 mb-2">
                <mdb-card-body class="p-2">
                  <mdb-card-text class="black-text"
                    >Qui animi molestiae autem nihil optio recusandae nisi sit ab quo est.
                  </mdb-card-text>
                </mdb-card-body>
              </mdb-card>
            </div>
            <mdb-card bgColor="bg-primary" class="rounded w-75 float-right z-depth-0 mb-2">
              <mdb-card-body class="p-2">
                <mdb-card-text class="text-white"
                  >Maxime nostrum ut blanditiis a quod quam, quidem deleniti?
                </mdb-card-text>
              </mdb-card-body>
            </mdb-card>
          </div>
        </mdb-card-body>
      </div>
      <mdb-card-footer class="text-muted white pt-1 pb-2 px-3">
        <input
          type="text"
          id="exampleForm2"
          class="form-control"
          placeholder="Type a message..."
        />
        <div>
          <a>
            <mdb-icon far icon="file-image" class="mr-2"></mdb-icon>
          </a>
          <a>
            <mdb-icon far icon="laugh" class="mr-2"></mdb-icon>
          </a>
          <a>
            <mdb-icon fas icon="gamepad" class="mr-2"></mdb-icon>
          </a>
          <a>
            <mdb-icon fas icon="paperclip" class="mr-2"></mdb-icon>
          </a>
          <a>
            <mdb-icon fas icon="camera" class="mr-2"></mdb-icon>
          </a>
          <a>
            <mdb-icon fas icon="thumbs-up" class="float-right"></mdb-icon>
          </a>
        </div>
      </mdb-card-footer>
    </mdb-card>

In SCSS change position: fixed to position: relative and remove bottom: 0 from the chat.room.small-chat rule:

.chat-room.small-chat {
  position: relative;
  -webkit-border-bottom-left-radius: 0;
  border-bottom-left-radius: 0;
  -webkit-border-bottom-right-radius: 0;
  border-bottom-right-radius: 0;
  width: 20rem;
}