JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
            <div id="fixed-header">
                User Infos
            </div>
          
            
            <div class="st-container">
            
                <input type="radio" name="radio-set" checked="checked" id="st-control-1"/>
                <a href="#st-panel-1">Serendipity</a>
                <input type="radio" name="radio-set" id="st-control-2"/>
                <a href="#st-panel-2">Happiness</a>
                <input type="radio" name="radio-set" id="st-control-3"/>
                <a href="#st-panel-3">Tranquillity</a>
                <input type="radio" name="radio-set" id="st-control-4"/>
                <a href="#st-panel-4">Positivity</a>
                <input type="radio" name="radio-set" id="st-control-5"/>
                <a href="#st-panel-5">Passion</a>
                
                <div class="st-scroll">
              
                    
                    <div class="st-panel" id="st-panel-1">
                        <h2>Serendipity</h2>
                        <p>Banksy adipisicing eiusmod banh mi sed. Squid stumptown est odd future nisi, commodo mlkshk pop-up adipisicing retro.</p>
                    </div >
           <!--problematic section starts-->         
       <div id="RepresentativeRegistrationPage" class="st-panel st-color">
<form action="#" method="post" id="registration-form" novalidate="novalidate">
    College:
    <select class="required" id="college_id" name="college_id">
                    <option selected="selected" value="">Select College</option>
                                            <option value="4">St. Xaviers College</option>
                                                <option value="5">DMC College</option>
                        </select><span class="error_msg"></span><br>
    First Name: <input type="text" value="" class="required" name="first_name" id="first_name"><span class="error_msg"></span><br>
    Last Name: <input type="text" value=""...

CSS

#fixed-header {
    position: fixed;
    width: 100%;
    top: 0;
    height: 100px;
    background: red
}

.st-container {
    position: absolute;
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    font-family: 'Josefin Slab', 'Myriad Pro', Arial, sans-serif;
}

.st-container > input,
.st-container > a {
    position: fixed;
    bottom: 0px;
    width: 20%;
    cursor: pointer;
    font-size: 16px;
    height: 34px;
    line-height: 34px;
}

.st-container > input {
    opacity: 0;
    z-index: 1000;
}

.st-container > a {
    z-index: 10;
    font-weight: 700;
    background: #e23a6e;
    color: #fff;
    text-align: center;
    text-shadow: 1px 1px 1px rgba(151,24,64,0.2);
}

/* "Fix" for percentage rounding: add a background bar pseudo element with the same color like the labels */
.st-container:before {
    content: '';
    position: fixed;
    width: 100%;
    height: 34px;
    background: #e23a6e;
    z-index: 9;
    bottom: 0;
}

#st-control-1, #st-control-1 + a {
    left: 0;
}

#st-control-2, #st-control-2 + a {
    left: 20%;
}

#st-control-3, #st-control-3 + a {
    left: 40%;
}

#st-control-4, #st-control-4 + a {
    left: 60%;
}

#st-control-5, #st-control-5 + a {
    left: 80%;
}

.st-container > input:checked + a,
.st-container > input:checked:hover + a{
    background: #821134;
}

.st-container > input:checked + a:after,
.st-container > input:checked:hover + a:after{
    bottom: 100%;
    border: solid transparent;
    content: '';
    height: 0;
    width: 0;
    position: absolute;
    pointer-events: none;
    border-bottom-color: #821134;
    border-width: 20px;
    left: 50%;
    margin-left: -20px;
}

.st-container > input:hover + a{
    background: #AD244F;
}

.st-container > input:hover + a:after {
    border-bottom-color: #AD244F;
}

.st-scroll,
.st-panel {
    position: relative;
    width: 100%;
    height: 100%;
}

.st-scroll {
    top: 0;
    left: 0;
    -webkit-transition: all 0.6s ease-in-out;
    -moz-transition: all...

JavaScript

var tabs = document.getElementById("registration-form").elements;
for (var i = 0; i < tabs.length; i++) {
    tabs[i].setAttribute("tabindex", i + 1);
    tabs[i].addEventListener('keydown', function(e) {
        var e = window.event || e;
        var keyCode = e.keyCode || e.which;

        if (keyCode == 9) {
            e.preventDefault();

            var x = window.scrollX,
                y = window.scrollY;

            var elementToFocus = document.getElementById("registration-form").elements[this.getAttribute("tabindex")];
            if (typeof elementToFocus == "undefined") {
                elementToFocus = document.getElementById("registration-form").elements[0];
            }
            elementToFocus.focus();
            window.scrollTo(x, y);

        }
    });
}
window.addEventListener("scroll", function(e) {
    var e = window.event || e;
    e.preventDefault();
    window.scrollTo(0, 0);
});