JSFiddle - React, Tailwind, and code Playground

by Michel Penke

HTML

<div id="btn-lokal-anmelden">

</div>

CSS

#btn-lokal-anmelden {

  height: 100px;
  width: 100px;
  background-color: blue;

}
#form-anmelden {
  height: 0px;
  width: 100%;
  background-color: red;
}

JavaScript

document.getElementById('btn-lokal-anmelden').onclick=function(){
  // Remove any element-specific value, falling back to stylesheets
  document.getElementById('form-anmelden').style.height='100px';
};