JSFiddle - React, Tailwind, and code Playground

HTML

<div class="checkbox">
    <input id="check" name="checkbox" type="checkbox">
    <label for="checkbox">
      Some Text Here
    </label>
  </div>
  <input type="submit" name="anmelden" class="button" id="btncheck" value="Send" />

CSS

* {margin: 0px; padding: 0px;}
body {background-color: rgb(248,248,248)}
#nav {
    list-style:none;
}
#nav li {
    float:left;
    display:block;
    width:100px;
    position:relative;
    z-index:500;
}
/* this is the parent menu */
 #nav li a {
    display:block;
    padding:15px;
    color:#000;
    border: 1px solid transparent;
}
#nav li a:hover {
    border: 1px solid black;
    
}
 #nav a.open {
    color:#fff;
    background-color: pink;
}
 #nav ul {
    position:absolute;
    display:none;
    padding:0;
    list-style:none;
}
#nav ul li {
    width:100px;
    float:left;
}
 #nav ul a {
    display:block;
    height:15px;
    padding: 15px;
    color:#666;
}
#nav ul a:hover {
    text-decoration:underline;
}
.active{
    background-color: pink;
    
}

JavaScript

$('#check').click(function(){

    if(!$(this).is(':checked')){
     $('#btncheck').attr("disabled","disabled");   
}
else
    $('#btncheck').removeAttr('disabled');
});