<!DOCTYPE html> <meta name="viewport" content="width=device-width,initial-scale=1"> <style> html, body { margin: 0; width: 100%; height: 100%; } div { position: absolute; } </style> <div style="background: green; width: 100%; height: 100%;"></div> <div style="background: blue; width: 50%; height: 50%;"></div>