<style> body { overflow-x: scroll } div { width: 10px; height: 10px; background-color: #d64203; } </style> <body> <div style="width: 50px"></div> <!-- Unaffected by scrollbars. --> <div id="b"></div> <div style="width: 35px"></div> <!-- Unaffected by scrollbars. --> <div id="d"></div> <!-- Deliberately make scrollbars appear. --> <div style="width: 500px; height: 500px; background-color: black"> </body> <script> // client{Width, Height} consist of the area _inside_ the scrollbars, so these // manually calculated units reflect the fact that with 'overflow: scroll' set, // viewport units are sized taking the scrollbars into account. Since we're // only dealing with 'overflow-x' here, only the height units are affected. var vh = 0.01 * document.body.clientHeight; document.getElementById('b').style.height = (25 * vh) + "px"; document.getElementById('d').style.height = (25 * vh) + "px"; </script>