CSS Hamburger stops working when jQuery library is loaded into project

Question

I am trying to utilize CSS for a responsive hamburger menu and the jQuery for some drop down menu items further down my webpage. The CSS hamburger menu works perfectly fine when I don't have the jQuery library loaded into my project. However as soon as I do load in the jQuery library the CSS hamburger stops working. I am not getting any error messages. How do I fix this?

This is my first question in the stackoverflow community am I am a beginner with coding. Any and all help is appreciated.

Hamburger in index.html:

</head>
    <header class="header">
      <a href="" class="logo"><img src="./img/consulting.png" alt=""><h1><span class ="highlight"></span> 
       Consulting</h1></a>
      <input class="menu-btn" type="checkbox" id="menu-btn"/>
      <label class="menu-icon" for="menu-btn"><span class="navicon"></span></label>
      <ul class="menu">
        <li><a href="services.html">Services</a></li>
        <li><a href="#careers">Careers</a></li>
        <li><a href="#contact">Contact</a></li>
      </ul>
</header>

<script src="https://code.jquery.com/jquery-1.12.4.min.js"></script>

Hamburger in style.css:

    body {
  font-family: Arial, Helvetica, sans-serif;
  font-size:12px;
  line-height:1.5;
  padding:0;
  margin:0;
  background-color:#f4f4f4;
}

a {
  color: #000;
}

.header h1 {
  font-family: Arial, Helvetica, sans-serif;
  font-size:24px;
  font-weight: bold;
  width: 300px;
  margin-top: 12px;
  margin-bottom: 5px;
}
/*Global*/
.container{
  width:100%;
  margin:auto;
  overflow:hidden;
}
/* header */

.header {
  background-color: #fff;
  box-shadow: 1px 1px 4px 0 rgba(0,0,0,.1);
  position: fixed;
  width: 100%;
  border-bottom: #e8491d 3px solid;
  z-index: 3;
}

.header img {
float: left;
width: 60px;
height: 60px;
margin-bottom: 5px;
margin-right: 5px;
}

.header ul {
  margin: 0;
  padding: 0;
  list-style: none;
  overflow: hidden;
  background-color: #fff;
}

.header li a {
  display: block;
  margin-top: 5px;
  padding: 10px 30px;
  border-right: 1px solid #f4f4f4;
  text-decoration: none;
}

.header li a:hover,
.header .menu-btn:hover {
  background-color: #f4f4f4;
}

.header .logo {
  display: block;
  float: left;
  font-size: 2em;
  padding-left: 10px;
  padding-right: 5px;
  padding-top: 5px;
  text-decoration: none;
}

/* menu */

.header .menu {
  clear: both;
  max-height: 0;
  transition: max-height .2s ease-out;
}

/* menu icon */

.header .menu-icon {
  cursor: pointer;

  float: right;
  padding-top: 35px;
  padding-bottom: 35px;
  padding-left: 10px;
  padding-right: 20px;
  position: relative;
  user-select: none;
}

.header .menu-icon .navicon {
  background: #333;
  display: block;
  height: 2px;
  position: relative;
  transition: .2s ease-out;
  width: 18px;
}

.header .menu-icon .navicon:before,
.header .menu-icon .navicon:after {
  background: #333;
  content: '';
  display: block;
  height: 100%;
  position: absolute;
  transition: .2s ease-out;
  width: 100%;
}

.header .menu-icon .navicon:before {
  top: 5px;
}

.header .menu-icon .navicon:after {
  top: -5px;
}

/* menu btn */

.header .menu-btn {
  display: none;
}

.header .menu-btn:checked ~ .menu {
  max-height: 300px;
}

.header .menu-btn:checked ~ .menu-icon .navicon {
  background: transparent;
}

.header .menu-btn:checked ~ .menu-icon .navicon:before {
  transform: rotate(-45deg);
}

.header .menu-btn:checked ~ .menu-icon .navicon:after {
  transform: rotate(45deg);
}

.header .menu-btn:checked ~ .menu-icon:not(.steps) .navicon:before,
.header .menu-btn:checked ~ .menu-icon:not(.steps) .navicon:after {
  top: 0;
}

/* 48em = 768px */

@media (min-width: 48em) {
  .header li {
    float: left;
  }
  .header li a {
    padding: 23px 30px;
    margin-top: 5px;
  }
  .header .menu {
    clear: none;
    float: right;
    max-height: none;
  }
  .header .menu-icon {
    display: none;
    padding-left: 5px;
    padding-right: 5px;
  }

}