ao adicionar a propriedade fixed-top na navbar o movimento de colapsar e descolapsar não empurra as imagens para baixo, ao invés disso o menu de navegação fica por cima das imagens, no modo responsivo , o que pode ser?
<header>
<nav class="navbar navbar-expand-lg navbar-light bg-light fixed-top">
<a class="navbar-brand fonte-titulo-nome" href="#">Guia dos Cães</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarNavAltMarkup" aria-controls="navbarNavAltMarkup" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse justify-content-end" id="navbarNavAltMarkup">
<ul class="navbar-nav">
<li><a class="nav-item nav-link active" href="#">Home <span class="sr-only">(current)</span></a>
<li><a class="nav-item nav-link" href="#">Sobre Nos</a></li>
<li><a class="nav-item nav-link" href="#">Serviços</a></li>
<li><a class="nav-item nav-link" href="#">Galeria</a></li>
<li><a class="nav-item nav-link" href="#">Video</a></li>
<li><a class="nav-item nav-link" href="#">contato</a></li>
</ul>
</div>
</nav>
</header>
<main>
<section class="carrossel">
<div id="carouselExampleCaptions" class="carousel slide" data-interval="3000" data-ride="carousel">
<ol class="carousel-indicators">
<li data-target="#carouselExampleCaptions" data-slide-to="0" class="active"></li>
<li data-target="#carouselExampleCaptions" data-slide-to="1"></li>
<li data-target="#carouselExampleCaptions" data-slide-to="2"></li>
</ol>
<div class="carousel-inner">
<div class="carousel-item active zoom">
<img src="img/dogs.jpg" class="d-block w-100 imagem-carrossel p-1" alt="...">
<div class="carousel-caption d-none d-md-block h-50">
<h1 class="fonte-titulo" class="display-4">First slide label</h1>
<p>Nulla vitae elit libero, a pharetra augue mollis interdum.</p>
</div>
</div>
<div class="carousel-item zoom">
<img src="img/cachorro.jpg" class="d-block w-100 imagem-carrossel p-1" alt="...">
<div class="carousel-caption d-none d-md-block h-50">
<h1 class="fonte-titulo" class="display-4">Second slide label</h1>
<p>Lorem ipsum dolor sit amet, consectetur adipiscing elit.</p>
</div>
</div>
<div class="carousel-item zoom">
<img src="img/caes-calmos-7.jpg" class="d-block w-100 imagem-carrossel p-1" alt="...">
<div class="carousel-caption d-none d-md-block h-50">
<h1 class="fonte-titulo" class="display-4">Third slide label</h1>
<p>Praesent commodo cursus magna, vel scelerisque nisl consectetur.</p>
</div>
</div>
</div>
<a class="carousel-control-prev" href="#carouselExampleCaptions" 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="#carouselExampleCaptions" role="button" data-slide="next">
<span class="carousel-control-next-icon" aria-hidden="true"></span>
<span class="sr-only">Next</span>
</a>
</div>
</section>
