my slider takes up the whole screen what should I do

I wanted to use the slider as banner pictures 800 x 400 but the slider is getting full screen when i want to test this is the code I wrote Where will I write sizing?

[CODE]

              </div>
              <div class="carousel-item">
                <img src="images/banner2.jpg" class="d-block w-100" alt="...">
              </div>
              <div class="carousel-item">
                <img src="images/banner3.jpg" class="d-block w-100" alt="...">
              </div>
            </div>
            <a class="carousel-control-prev" href="#carouselExampleControls" role="button" data-slide="prev">
              <span class="carousel-control-prev-icon" aria-hidden="true"></span>
              <span class="sr-only">Previous</span>
            </a>
            <a class="carousel-control-next" href="#carouselExampleControls" role="button" data-slide="next">
              <span class="carousel-control-next-icon" aria-hidden="true"></span>
              <span class="sr-only">Next</span>
            </a>
          </div>

[CODE]