scroll inside on rotate 90deg

dabblet.css

/**
 * The first commented line is your dabblet’s title
 */

html, body {
	background: #f06;
	height: 100%;
}

#ctn {
	width: 100%;
	height: 100%;
	transform: rotate(90deg);
	overflow-x: auto;
	overflow-y: hidden;
}

dabblet.html

<div id="ctn">
  hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello hello
</div>

dabblet.js

// alert('Hello world!');

settings.json

{"view":"split-vertical","fontsize":"100","seethrough":"","prefixfree":"1","page":"all"}