The css that contributed qwerty is applied and remains that way.
@media (max-width: 767px) {
.display-4 {
font-size: 1.3em !important;
}
h4 {
font-size: 1em !important;
}<!doctype html>
<html lang="es">
<head>
<!-- Required meta tags -->
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
<!-- Bootstrap CSS -->
<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.2.1/css/bootstrap.min.css" integrity="sha384-GJzZqFGwb1QTTN6wy59ffF1BuGJpLSa9DkKMp0DgiMDm4iYMj70gZWKYbI706tWS" crossorigin="anonymous">
<!-- Archivos Personales -->
<link rel="stylesheet" href="files/css/main.css">
<title>Madiweb</title>
</head>
<body>
<!-- Menu Principal -->
<nav class="navbar fixed-top navbar-expand-lg navbar-light bg-light">
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarText" aria-controls="navbarText" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
<div class="collapse navbar-collapse" id="navbarText">
<ul class="navbar-nav ml-5 mr-auto">
<li class="nav-item active mr-3">
<a class="nav-link" href="#">Inicio <span class="sr-only">(current)</span></a>
</li>
<li class="nav-item mr-3">
<a class="nav-link" href="#">Empresa</a>
</li>
<li class="nav-item mr-3">
<a class="nav-link" href="#">Servicios</a>
</li>
<li class="nav-item">
<a class="nav-link" href="#">Contacto</a>
</li>
</ul>
<!-- Barra Contacto -->
<span class="navbar-text mr-5 text-body">
(+54) 03725 - 15440397 | [email protected]
</span>
</div>
</nav>
<!-- Portada -->
<div id="carouselExampleIndicators" class="carousel slide" style="margin-top: 3.5rem;" data-ride="carousel">
<ol class="carousel-indicators">
<li data-target="#carouselExampleIndicators" data-slide-to="0" class="active"></li>
</ol>
<div class="carousel-inner">
<div class="carousel-item active">
<img src="https://td2branding.com/wp-content/uploads/2018/08/Fondo-Amco-1920-x-800-1.jpg" class="d-block w-100" alt="portada-1">
<div class="carousel-caption d-block">
<div class="display-4">DISEÑO WEB A MEDIDA</div>
<hr class="my-2 bg-white">
<h4>Somos diseñadores de web, analizamos cada proyecto y presentamos la mejor opción para cada necesidad, brindando sitios funcionales de calidad.</h4>
</div>
</div>
</div>
</div>
<!-- Optional JavaScript -->
<!-- jQuery first, then Popper.js, then Bootstrap JS -->
<script src="https://code.jquery.com/jquery-3.3.1.slim.min.js" integrity="sha384-q8i/X+965DzO0rT7abK41JStQIAqVgRVzpbzo5smXKp4YfRvH+8abtTE1Pi6jizo" crossorigin="anonymous"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.6/umd/popper.min.js" integrity="sha384-wHAiFfRlMFy6i5SRaxvfOCifBUQy1xHdJ/yoi7FRNXMRBu5WHdZYu1hA6ZOblgut" crossorigin="anonymous"></script>
<script src="https://stackpath.bootstrapcdn.com/bootstrap/4.2.1/js/bootstrap.min.js" integrity="sha384-B0UglyR+jN6CkvvICOB2joaf5I4l3gm9GU6Hc1og6Ls7i6U/mkkaduKaBhlAXv9k" crossorigin="anonymous"></script>
</body>
</html>