HTML structures, CSS styles, and JavaScript behaves. It runs in every browser with no install, reacting to clicks, fetching data, and rewriting the page live. The same language now also runs servers (Node), build tools, and apps. Learn it and you can move from static pages to real software.
<!doctype html><html><head><meta charset="utf-8"></head>
<body style="background:#06040d;color:#e6e0ff;font-family:sans-serif;padding:20px">
<h1 id="h">static</h1><button id="b">make it interactive</button>
<script>document.getElementById('b').onclick=()=>document.getElementById('h').textContent='now dynamic';</script></body></html>