Div overlaps Nav

I have the following problem: I am trying to modulate the system by applying the MVC pattern, and on the one hand I have a file phpfor the header of the page, another for the footer and another for the content. Everything was going well until, when trying to put a content like the one shown in the example, it overlaps the nav and is placed at the top left of the page, as if it had 0 margin top and left.

I want whatever the content was to be placed where it should be, which is below the navigation bar. Any suggestion?

A header.php

       <nav class="navbar navbar-light navbar-expand-md justify-content-center fixed-top pt-0 w-100" id="navigation-bar">
            <div class="container">

                <div class="navbar-collapse collapse justify-content-between align-items-center w-100 " id="collapsingNavbar2">
                    <ul class="topBotomBordersOut navbar-nav mx-auto text-center">
                        <li class="nav-item active pt-4">
                            <a class="nav-link" href="#">Home</a>
                        </li>
                        <li class="nav-item pt-4">
                            <a class="nav-link" href="#">My Glossaries</a>
                        </li>
                        <li class="nav-item pt-4">
                            <a class="nav-link" href="#">Al Glossaries</a>
                        </li>
                    </ul>
                </div>

            </div>
            <div class="navbar-custom-menu float-lg-right">
                <ul class="nav topBotomBordersOut navbar-nav mx-auto text-center">
                    <li class="nav-item pt-4">
                        <a href="#" class="nav-link" data-toggle="dropdown" id="user-button">
                                <img src="" class="user-image">
                                <span class="hidden-xs">Logout</span>

                        </a>

                    </li>
                </ul>
            </div>
        </nav>

And a content.php

<div class="content">

<div class="row">
    <div class="col-4">Aca iria</div>
    <div class="col-4">El contenido</div>
    <div class="col-4">Principal</div>
</div>

I also add everything just cssin case

@import url(http://fonts.googleapis.com/css?family=Numans);
html,
body {
    background-color: #D8A7B1;
    height: 100%;
    font-family: 'Numans', sans-serif;
    }

a {
    color: #fff !important;
}

.nav-item {
    font-family: Century Gothic;
    margin: 0 auto;
    padding: 5em 3em;
    text-align: center;
}

.nav-item a {
    color: #FFF;
    text-decoration: none;
    font: 20px Century Gothic;
    margin: 0px 10px;
    padding: 10px 10px;
    position: relative;
    z-index: 0;
}


/* Top & Bottom Borders Out */

.topBotomBordersOut a:before,
.topBotomBordersOut a:after {
    position: absolute;
    left: 0px;
    width: 100%;
    height: 2px;
    background: #FFF;
    content: "";
    opacity: 0;
    -webkit-transition: all 0.3s;
    transition: all 0.3s;
}

.topBotomBordersOut a:before {
    top: 0px;
    transform: translateY(10px);
}

.topBotomBordersOut a:after {
    bottom: 0px;
    transform: translateY(-10px);
}

.topBotomBordersOut a:hover:before,
.topBotomBordersOut a:hover:after {
    opacity: 1;
    transform: translateY(0px);
}

.container {
    height: 100%;
    align-content: center;
    position: relative;
}

.card {
    height: 370px;
    margin-top: auto;
    margin-bottom: auto;
    width: 400px;
    background-color: rgba(0, 0, 0, 0.5) !important;
}

.social_icon span {
    font-size: 60px;
    margin-left: 10px;
    color: #FAE8E0;
}

.social_icon span:hover {
    color: white;
    cursor: pointer;
}

.card-header h3 {
    color: white;
}

.social_icon {
    position: absolute;
    right: 20px;
    top: -45px;
}

.input-group-prepend span {
    width: 50px;
    background-color: #FAE8E0;
    ;
    color: black;
    border: 0 !important;
}

input:focus {
    outline: 0 0 0 0 !important;
    box-shadow: 0 0 0 0 !important;
}

.remember {
    color: white;
}

.remember input {
    width: 20px;
    height: 20px;
    margin-left: 15px;
    margin-right: 5px;
}

.login_btn {
    color: black;
    background-color: #FAE8E0;
    width: 100px;
}

.login_btn:hover {
    color: black;
    background-color: white;
}

.links {
    color: white;
}

.links a {
    margin-left: 4px;
}

#user-button {
    text-decoration: none;
}

.navigation-bar {
    position: absolute;
}

.content {
    position: relative;
}