Bootstrap 4: Footer not at bottom
If you want a fixed footer, just add the class fixed-bottom to the footer tag like shown below.
<footer class="fixed-bottom bg-dark">
<div class="text-center">
<p>Footer</p>
</div>
</footer>
You can use built-in bootstrap class to achieve this.
What you need is the container to be a column flex container . class to use are : d-flex flex-column
To set the container to height:100% you can apply the class h-100to html, body and the container or add to the container style height:100vh;
For the footer, a margin-top:auto will do, the class to use is : mt-auto;
example below to run in full page mode
<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/4.5.0/css/bootstrap.min.css" rel="stylesheet"/>
<html class="h-100">
<body class="h-100">
<!-- Page Container -->
<div id="page-container" class="container-fluid pr-0 pl-0 h-100 d-flex flex-column">
<!-- Header -->
<nav class="navbar navbar-expand-lg navbar-light bg-light pt-3 pb-3 d-flex justify-content-center">
<div class="col-md-8 col-lg-8 col-sm-12 col-xs-12 d-flex justify-content-between">
<div class="d-flex justify-content-start align-items-center">
<a href="/" class="kf-links">
<span class="h5">
<i class="fas fa-paper-plane"></i>
<span class="h4 font-weight-bold kf-dark">
MyPage
</span>
</span>
</a>
</div>
<!-- Main Header Navigation -->
<div class="collapse navbar-collapse justify-content-end" id="navbarSupportedContent">
<ul class="navbar-nav">
<li class="nav-item">
<a href="/" class="nav-link ">Link1</a>
</li>
<li class="nav-item">
<a href="" class="nav-link ">Link2</a>
</li>
<li class="nav-item">
<a href="" class="nav-link ">Link3</a>
</li>
</ul>
</div>
<!-- END Main Header Navigation -->
</div>
</nav>
<!-- END Header -->
<!-- Main Container -->
<div style="background:#5c90d2">
<div class="col-md-12 text-center pt-5 pb-5">
<div class="pt-5 pb-5">
<h1>
<span class="main-text">
Login
</span>
</h1>
<p class="lead"><span class="main-text">
Login Now!
</span></p>
</div>
</div>
</div>
<!-- Content -->
<div class="d-flex justify-content-center fadeIn">
<div class="col-md-8 col-xs-12">
<div class="d-flex justify-content-center">
<div class="col-md-6 pt-5 pb-5 pr-0 pl-0">
<form class="form-horizontal" method="post">
<div class="form-group">
<div class="col-xs-12">
<div class="">
<label for="id_username">E-Mail</label>
<input id="id_username" class="form-control" maxlength="254" name="username" value="" type="text" required>
</div>
</div>
</div>
<div class="form-group">
<div class="col-xs-12">
<div class="">
<label for="id_password">Password</label>
<input id="id_password" class="form-control" name="password" type="password" required>
</div>
</div>
</div>
<div class="form-group">
<div class="col-xs-12">
<small class="float-right">
<a href="#" class="kf-links">Forgot Password?</a>
</small>
</div>
</div>
<div class="form-group mt-5">
<div class="col-xs-12 col-sm-6 col-sm-offset-3 col-md-4 col-md-offset-4 pl-0">
<button class="btn btn-sm btn-block btn-primary" type="submit">Login</button>
</div>
</div>
</form>
</div>
</div>
</div>
</div>
<!-- END Content -->
<!-- END Main Container -->
<!-- Footer -->
<footer class="d-flex justify-content-center mt-auto">
<div class="d-flex justify-content-between col-md-8 col-md-offset-2 mb-3 mt-5">
<!-- Copyright Info -->
<div class="align-left">
<a class="font-weight-bold small kf-blue kf-links" href="#">Link1</a> |
<a class="font-weight-bold small kf-blue kf-links" href="/">Link2</a> |
<a class="font-weight-bold small kf-blue kf-links" href="/">Link3</a>
</div>
<div class="align-right small">
Crafted with Love by <a class="font-weight-bold kf-blue kf-links" href="#" target="_blank">Me</a>
</div>
<!-- END Copyright Info -->
</div>
</footer>
<!-- END Footer -->
</div>
<!-- END Page Container -->
</body>
</html>codepen updated https://codepen.io/anon/pen/PBpgNN
reminder for boostrap classes https://getbootstrap.com/docs/4.5/utilities/flex/ about sizing see https://getbootstrap.com/docs/4.5/utilities/sizing/
First add display: flex; and flex-direction: column; to #page-container.
Now you have "set the stage" for aligning the footer to the bottom. Set its margin-top to auto (by adding the class mt-auto) and you are done;
<div class="d-flex justify-content-center mt-auto">
Content here
</div>
See this codepen.