The first commented line is your dabblet’s title

dabblet.css

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

html {
	font-family: georgia, sans-serif;
	font-size: 100%;
}
h1 {
	font-size: 1.2em;
	font-weight: normal;
}

dabblet.html

<h1>Does it really matter how big this header is in <em>pixels</em>?</h1>
<p>No, it doesn't. What matters is if the contrast between this paragraph and the header is big enough. If people will be able to see the difference between a <code>h1</code>, a <code>h2</code> and a <code>p</code>.
 That's what matters. In this case I'd say the <code>h1</code> is too small. I'd try a value of <code>1.414em</code>, or <code>2.9em</code>. Whatever looks good. Remember the first time you worked with pixels? You had no idea how big <code>300px</code> was exactly. You got used to it. You'll get used to other units as well.

dabblet.js

// alert('Hello world!');

settings.json

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