How to apply dark or night mode in a blog or website?

Question

I want html js, java and css for dark mode or night mode, that is not going to off on on refreshing the page, and remains dark or light or night mode until again button pressed.

Answer 1

I will write here some code for bloggers to apply night mode on own blogs... check this on my blog Science in Hindi working well.. 100% working, and dark mode is not going to off when you refresh the page.. that is not going to off on refreshing the page, and remains dark or light or night mode until again button pressed.

<!-- Theme Functions JS -->
<script type='text/javascript'>
//<![CDATA[
function retheme() {
  var cc = document.body.className;
  if (cc.indexOf("darktheme") > -1) {
    document.body.className = cc.replace("darktheme", "");
    if (opener) {opener.document.body.className = cc.replace("darktheme", "");}
    localStorage.setItem("preferredmode", "light");
  } else {
    document.body.className += " darktheme";
    if (opener) {opener.document.body.className += " darktheme";}
    localStorage.setItem("preferredmode", "dark");
  }
}
(
function setThemeMode() {
  var x = localStorage.getItem("preferredmode");
  if (x == "dark") {
    document.body.className += " darktheme";
  }
})();
//]]>
</script>

<!-- theme switch is a button icon adjust this as your icon stylesheet -->
#theme-switch{font-size:20px;position:absolute;top:0;right:35px;z-index:19}
<!-- Here is your stylesheet for dark mode editd these colors and style name except body darktheme -->
body.darktheme{color:#fff;background-color:#000}
body.darktheme .your-element-name{color:#fff;background-color:#000}
body.darktheme .lin-element-name a{color:#fff;background-color:#000}
body.darktheme #your-element-name{color:#fff;background-color:#000}
body.darktheme your-element-name ul li a{color:#fff;background-color:#000}

<div id='theme-switch'>
<a class='fa fa-adjust' href='javascript:void(0);' onclick='retheme()' title='Change Theme'/>
    </div>