i need to add cookies to my modal popup to be visible only once for user per browser session in all project web pages.
here is the HTML Code
    <div id="popup">
    <div class="modalconent">
      <button id="button"><span class="close">×</span></button>
         <h1></h1>
        <p>Some text in the Modal..</p>
    </div>
</div> 
and here is my javascript code:
window.onload = function () {
  document.getElementById('button').onclick = function () {
      document.getElementById('popup').style.display = "none"
  };
};
and here is my css code:
#modal {
    position: fixed;
    font-family: Arial, Helvetica, sans-serif;
    top: 0;
    left: 0;
    background: rgba(0, 0, 0, 0.8);
    z-index: 99999;
    height: 100%;
    width: 100%;
}
.modalconent {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background: #fff;
    width: 80%;
    padding: 20px;
}
