I am trying to learn frontend with bootstrap. I found out that I can combine CSS, HTML and Javascript in a single HTML file. However, when I load the page in the browser, nothing shows up. I tried testing the code online ( on w3schools) and the loaded page works fine. I am not sure if it helps but this is my code:

```html
<!DOCTYPE html>
<html>
<head>
<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<style>
/* BASIC */

html {
  background-color: #56baed;
}

body {
  font-family: "Poppins", sans-serif;
  height: 100vh;
}

a {
  color: #92badd;
  display:inline-block;
  text-decoration: none;
  font-weight: 400;
}

h2 {
  text-align: center;
  font-size: 16px;
  font-weight: 600;
  text-transform: uppercase;
  display:inline-block;
  margin: 40px 8px 10px 8px;
  color: #cccccc;
}

/* STRUCTURE */

.wrapper {
  display: flex;
  align-items: center;
  flex-direction: column;
  justify-content: center;
  width: 100%;
  min-height: 100%;
  padding: 20px;
}

#formContent {
  -webkit-border-radius: 10px 10px 10px 10px;
  border-radius: 10px 10px 10px 10px;
  background: #fff;
  padding: 30px;
  width: 90%;
  max-width: 450px;
  position: relative;
  padding: 0px;
  -webkit-box-shadow: 0 30px 60px 0 rgba(0,0,0,0.3);
  box-shadow: 0 30px 60px 0 rgba(0,0,0,0.3);
  text-align: center;
}

#formFooter {
  background-color: #f6f6f6;
  border-top: 1px solid #dce8f1;
  padding: 25px;
  text-align: center;
  -webkit-border-radius: 0 0 10px 10px;
  border-radius: 0 0 10px 10px;
}

/* TABS */

h2.inactive {
  color: #cccccc;
}

h2.active {
  color: #0d0d0d;
  border-bottom: 2px solid #5fbae9;
}

/* FORM TYPOGRAPHY*/

input[type=button], input[type=submit], input[type=reset]  {
  background-color: #56baed;
  border: none;
  color: white;
  padding: 15px 80px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  text-transform: uppercase;
  font-size: 13px;
  -webkit-box-shadow: 0 10px 30px 0 rgba(95,186,233,0.4);
  box-shadow: 0 10px 30px 0 rgba(95,186,233,0.4);
  -webkit-border-radius: 5px 5px 5px 5px;
  border-radius: 5px 5px 5px 5px;
  margin: 5px 20px 40px 20px;
  -webkit-transition: all 0.3s ease-in-out;
  -moz-transition: all 0.3s ease-in-out;
  -ms-transition: all 0.3s ease-in-out;
  -o-transition: all 0.3s ease-in-out;
  transition: all 0.3s ease-in-out;
}

input[type=button]:hover, input[type=submit]:hover, input[type=reset]:hover  {
  background-color: #39ace7;
}

input[type=button]:active, input[type=submit]:active, input[type=reset]:active  {
  -moz-transform: scale(0.95);
  -webkit-transform: scale(0.95);
  -o-transform: scale(0.95);
  -ms-transform: scale(0.95);
  transform: scale(0.95);
}

input[type=text] {
  background-color: #f6f6f6;
  border: none;
  color: #0d0d0d;
  padding: 15px 32px;
  text-align: center;
  text-decoration: none;
  display: inline-block;
  font-size: 16px;
  margin: 5px;
  width: 85%;
  border: 2px solid #f6f6f6;
  -webkit-transition: all 0.5s ease-in-out;
  -moz-transition: all 0.5s ease-in-out;
  -ms-transition: all 0.5s ease-in-out;
  -o-transition: all 0.5s ease-in-out;
  transition: all 0.5s ease-in-out;
  -webkit-border-radius: 5px 5px 5px 5px;
  border-radius: 5px 5px 5px 5px;
}

input[type=text]:focus {
  background-color: #fff;
  border-bottom: 2px solid #5fbae9;
}

input[type=text]:placeholder {
  color: #cccccc;
}

/* ANIMATIONS */

/* Simple CSS3 Fade-in-down Animation */
.fadeInDown {
  -webkit-animation-name: fadeInDown;
  animation-name: fadeInDown;
  -webkit-animation-duration: 1s;
  animation-duration: 1s;
  -webkit-animation-fill-mode: both;
  animation-fill-mode: both;
}

@-webkit-keyframes fadeInDown {
  0% {
opacity: 0;
-webkit-transform: translate3d(0, -100%, 0);
transform: translate3d(0, -100%, 0);
  }
  100% {
opacity: 1;
-webkit-transform: none;
transform: none;
  }
}

@keyframes fadeInDown {
  0% {
opacity: 0;
-webkit-transform: translate3d(0, -100%, 0);
transform: translate3d(0, -100%, 0);
  }
  100% {
opacity: 1;
-webkit-transform: none;
transform: none;
  }
}

/* Simple CSS3 Fade-in Animation */
@-webkit-keyframes fadeIn { from { opacity:0; } to { opacity:1; } }
@-moz-keyframes fadeIn { from { opacity:0; } to { opacity:1; } }
@keyframes fadeIn { from { opacity:0; } to { opacity:1; } }

.fadeIn {
  opacity:0;
  -webkit-animation:fadeIn ease-in 1;
  -moz-animation:fadeIn ease-in 1;
  animation:fadeIn ease-in 1;

  -webkit-animation-fill-mode:forwards;
  -moz-animation-fill-mode:forwards;
  animation-fill-mode:forwards;

  -webkit-animation-duration:1s;
  -moz-animation-duration:1s;
  animation-duration:1s;
}

.fadeIn.first {
  -webkit-animation-delay: 0.4s;
  -moz-animation-delay: 0.4s;
  animation-delay: 0.4s;
}

.fadeIn.second {
  -webkit-animation-delay: 0.6s;
  -moz-animation-delay: 0.6s;
  animation-delay: 0.6s;
}

.fadeIn.third {
  -webkit-animation-delay: 0.8s;
  -moz-animation-delay: 0.8s;
  animation-delay: 0.8s;
}

.fadeIn.fourth {
  -webkit-animation-delay: 1s;
  -moz-animation-delay: 1s;
  animation-delay: 1s;
}

/* Simple CSS3 Fade-in Animation */
.underlineHover:after {
  display: block;
  left: 0;
  bottom: -10px;
  width: 0;
  height: 2px;
  background-color: #56baed;
  content: "";
  transition: width 0.2s;
}

.underlineHover:hover {
  color: #0d0d0d;
}

.underlineHover:hover:after{
  width: 100%;
}

/* OTHERS */

*:focus {
outline: none;
}

#icon {
  width:60%;
}

</style>
</head>
<body>

<div class="wrapper fadeInDown">
  <div id="formContent">
<!-- Tabs Titles -->

<!-- Icon -->
<div class="fadeIn first">
  <img src="http://danielzawadzki.com/codepen/01/icon.svg" id="icon" alt="User Icon" />
</div>

<!-- Login Form -->
<form>
  <input type="text" id="login" class="fadeIn second" name="login" placeholder="login">
  <input type="text" id="password" class="fadeIn third" name="login" placeholder="password">
  <input type="submit" class="fadeIn fourth" value="Log In">
</form>

<!-- Remind Passowrd -->
<div id="formFooter">
  <a class="underlineHover" href="#">Forgot Password?</a>
</div>

  </div>
</div>
</body>
</html>
```

Do you have any idea what is causing it to act this way?