/share/WebKit/editing/multiple.html

<head>
<meta name="viewport" content="width=device-width,initial-scale=1,maximum-scale=1,user-scalable=no">
<body>
<textarea placeholder="placeholder"></textarea>
<textarea placeholder="placeholder"></textarea>
<style>
:root {
	color-scheme: light dark;
}
body {
	display: flex;
	flex-direction: column;
}
textarea {
	flex-grow: 1;
	width: 100%;
	resize: none;
}
</style>