gatlin/index.html

## index.html
<!DOCTYPE html>
<html>
    <head>
        <title>Large Type</title>
        <link rel="stylesheet/less" type="text/css" href="style.less">
        <script type="text/javascript" src="lib/jquery-2.1.4.min.js"></script>
        <script type="text/javascript" src="lib/less.min.js"></script>
    </head>
    <body>
        <div class="out"><span contenteditable autofocus>*hello*</span></div>
        <div class="sidebar">
            <h1>Font</h1>
            <ul class="fonts">
                <li><input type="radio" name="font" data-font="Times New Roman" checked/></li>
                <li><input type="radio" name="font" data-font="Arial"/></li>
                <li><input type="radio" name="font" data-font="Courier"/></li>
            </ul>
        </div>
    </body>
    <script type="text/javascript" src="script.js"></script>
</html>

## script.js
$(document).ready(function() {
    /**
     * Minimum font size, in CSS pixels.
     */
    const MIN_SIZE = 10;

    var target = {
            el: $(".out"),
            text: undefined,
            h: undefined,
            w: undefined,
        },
        shadow = {
            el: target.el
                .clone()
                .addClass("shadow")
                .appendTo("body"),
        },
        size;

    target.text = target.el.children("span");
    shadow.text = shadow.el.children("span");
    setTarget();
    size = parseInt(target.el.css("font-size"));

    $(".out").on("keyup", function(event) {
        setText($(this).text());
    });

    $(window).on("resize", function() {
        setTarget();
    });

    $("input[name=font]").on("change", function(event) {
        var font = $(this).data("font");

        shadow.text.css("font-family", font);
        target.text.css("font-family", font);

        setText($(".out > span").text());
    });

    function setText(value) {
        if (value === "") {
            size = MIN_SIZE;
            finished();
            return;
        }

        shadow.text.text(value);

        // If there are newlines, don't wrap except on newlines.
        // Otherwise, wrap normally.
        setWrapping(value.indexOf("\n") >= 0 ?
                "pre" :
                "pre-wrap");

        // ±1 offset is to prevent bouncing between sizes
        var minSize = isBounded() ? size - 1 : MIN_SIZE,
            maxSize = isBounded() ? target.h : size + 1;

        while (maxSize - minSize > 1) {
            size = Math.floor((minSize + maxSize)/2);
            setSize();
            if (isBounded()) {
                minSize = size;
            } else {
                maxSize = size;
            }
        }

        finished();
    }

    function setWrapping(wrapping) {
        shadow.text.css("white-space", wrapping);
        target.text.css("white-space", wrapping);
    }

    function setSize() {
        shadow.text.css("font-size", size);
    }

    function finished() {
        target.text.css("font-size",size);
    }

    function isBounded() {
        return shadow.text.outerWidth() < target.w &&
            shadow.text.outerHeight() < target.h;
    }

    function setTarget() {
        target.h = target.el.innerHeight();
        target.w = target.el.innerWidth();
    }
});

## style.less
.out {
    position: absolute;
    text-align: center;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
    padding: 1em;
    margin: 0;
    overflow: hidden;

    & > span {
        font-family: serif;
        font-size: 100px;
        white-space: pre-wrap;
    }

    &:not(.shadow) > span {
        transition-property: font-size;
        transition-duration: 100ms;
        transition-timing-function: ease-in-out;
    }

    &.shadow {
        visibility: hidden;
    }
}

.sidebar {
    @border: 1px;
    @padding: 1em;

    position: absolute;
    top: 0;
    right: ~"calc( -25% - " @border ~" - " 2 * @padding ~")";
    bottom: 0;
    width: 25%;
    padding: 1em;
    margin: 0;
    background-color: whitesmoke;
    border-left: 1px solid grey;
    font-family: "Helvetica Neue", sans-serif;

    transition: right 250ms ease, box-shadow 100ms linear;

    & > ul {
        margin: 0;
        padding: 0;
        list-style-type: none;

        & > li {
            height: 2em;
            line-height: 2em;
            margin: 0 -1em;
            padding: 0 1em;
        }
    }

    & > h1 {
        height: 2em;
        line-height: 2em;
        margin: 0;
        padding: 0;
        font-size: medium;
    }

    &:hover {
        right: 0;
        box-shadow: 0 0 0.2em fade(black, 50%);
    }

    &:before {
        @color: grey;
        @height: 4em;

        position: absolute;
        font-size: 200%;
        color: @color;
        content: "«";
        top: ~"calc( 50% - " (@height + 2 * @padding/4) / 2 ~" - " 2 * @border ~")";
        left: -1em;
        padding: @padding/4;
        line-height: @height;
        border: @border solid @color;
        border-right: 0;
        border-radius: @padding/4;
        border-top-right-radius: 0;
        border-bottom-right-radius: 0;
        background-color: whitesmoke;
    }

    @media print {
        display: none;
    }
}

.sidebar .fonts {
    input {
        display: block;
        position: relative;
        font-family: attr(data-font);   // Doesn't work in Safari
        width: ~"calc( 100% + 2em )";
        height: 100%;
        line-height: 2em;
        margin: 0 -1em;
        padding: 0 1em;
        cursor: pointer;
        font-size: initial;

        // Make it look like not a radio element
        -webkit-appearance: none;

        &:after {
            content: attr(data-font);
            font-family: attr(data-font);
        }

        @shadow: 0 0 0.25em fade(black, 10%);

        &:hover, &:checked {
            background-color: lighten(whitesmoke,10%);
            box-shadow: @shadow;
        }

        &:checked {
            box-shadow: @shadow inset;
            cursor: initial;
        }
    }
}
	<!DOCTYPE html>
	<html>
	<head>
	<title>Large Type</title>
	<link rel="stylesheet/less" type="text/css" href="style.less">
	<script type="text/javascript" src="lib/jquery-2.1.4.min.js"></script>
	<script type="text/javascript" src="lib/less.min.js"></script>
	</head>
	<body>
	<div class="out"><span contenteditable autofocus>hello</span></div>
	<div class="sidebar">
	<h1>Font</h1>
	<ul class="fonts">
	<li><input type="radio" name="font" data-font="Times New Roman" checked/></li>
	<li><input type="radio" name="font" data-font="Arial"/></li>
	<li><input type="radio" name="font" data-font="Courier"/></li>
	</ul>
	</div>
	</body>
	<script type="text/javascript" src="script.js"></script>
	</html>
	$(document).ready(function() {
	/**
	* Minimum font size, in CSS pixels.
	*/
	const MIN_SIZE = 10;

	var target = {
	el: $(".out"),
	text: undefined,
	h: undefined,
	w: undefined,
	},
	shadow = {
	el: target.el
	.clone()
	.addClass("shadow")
	.appendTo("body"),
	},
	size;

	target.text = target.el.children("span");
	shadow.text = shadow.el.children("span");
	setTarget();
	size = parseInt(target.el.css("font-size"));

	$(".out").on("keyup", function(event) {
	setText($(this).text());
	});

	$(window).on("resize", function() {
	setTarget();
	});

	$("input[name=font]").on("change", function(event) {
	var font = $(this).data("font");

	shadow.text.css("font-family", font);
	target.text.css("font-family", font);

	setText($(".out > span").text());
	});

	function setText(value) {
	if (value === "") {
	size = MIN_SIZE;
	finished();
	return;
	}

	shadow.text.text(value);

	// If there are newlines, don't wrap except on newlines.
	// Otherwise, wrap normally.
	setWrapping(value.indexOf("\n") >= 0 ?
	"pre" :
	"pre-wrap");

	// ±1 offset is to prevent bouncing between sizes
	var minSize = isBounded() ? size - 1 : MIN_SIZE,
	maxSize = isBounded() ? target.h : size + 1;

	while (maxSize - minSize > 1) {
	size = Math.floor((minSize + maxSize)/2);
	setSize();
	if (isBounded()) {
	minSize = size;
	} else {
	maxSize = size;
	}
	}

	finished();
	}

	function setWrapping(wrapping) {
	shadow.text.css("white-space", wrapping);
	target.text.css("white-space", wrapping);
	}

	function setSize() {
	shadow.text.css("font-size", size);
	}

	function finished() {
	target.text.css("font-size",size);
	}

	function isBounded() {
	return shadow.text.outerWidth() < target.w &&
	shadow.text.outerHeight() < target.h;
	}

	function setTarget() {
	target.h = target.el.innerHeight();
	target.w = target.el.innerWidth();
	}
	});
	.out {
	position: absolute;
	text-align: center;
	top: 0;
	right: 0;
	bottom: 0;
	left: 0;
	padding: 1em;
	margin: 0;
	overflow: hidden;

	& > span {
	font-family: serif;
	font-size: 100px;
	white-space: pre-wrap;
	}

	&:not(.shadow) > span {
	transition-property: font-size;
	transition-duration: 100ms;
	transition-timing-function: ease-in-out;
	}

	&.shadow {
	visibility: hidden;
	}
	}

	.sidebar {
	@border: 1px;
	@padding: 1em;

	position: absolute;
	top: 0;
	right: ~"calc( -25% - " @border ~" - " 2 * @padding ~")";
	bottom: 0;
	width: 25%;
	padding: 1em;
	margin: 0;
	background-color: whitesmoke;
	border-left: 1px solid grey;
	font-family: "Helvetica Neue", sans-serif;

	transition: right 250ms ease, box-shadow 100ms linear;

	& > ul {
	margin: 0;
	padding: 0;
	list-style-type: none;

	& > li {
	height: 2em;
	line-height: 2em;
	margin: 0 -1em;
	padding: 0 1em;
	}
	}

	& > h1 {
	height: 2em;
	line-height: 2em;
	margin: 0;
	padding: 0;
	font-size: medium;
	}

	&:hover {
	right: 0;
	box-shadow: 0 0 0.2em fade(black, 50%);
	}

	&:before {
	@color: grey;
	@height: 4em;

	position: absolute;
	font-size: 200%;
	color: @color;
	content: "«";
	top: ~"calc( 50% - " (@height + 2 * @padding/4) / 2 ~" - " 2 * @border ~")";
	left: -1em;
	padding: @padding/4;
	line-height: @height;
	border: @border solid @color;
	border-right: 0;
	border-radius: @padding/4;
	border-top-right-radius: 0;
	border-bottom-right-radius: 0;
	background-color: whitesmoke;
	}

	@media print {
	display: none;
	}
	}

	.sidebar .fonts {
	input {
	display: block;
	position: relative;
	font-family: attr(data-font); // Doesn't work in Safari
	width: ~"calc( 100% + 2em )";
	height: 100%;
	line-height: 2em;
	margin: 0 -1em;
	padding: 0 1em;
	cursor: pointer;
	font-size: initial;

	// Make it look like not a radio element
	-webkit-appearance: none;

	&:after {
	content: attr(data-font);
	font-family: attr(data-font);
	}

	@shadow: 0 0 0.25em fade(black, 10%);

	&:hover, &:checked {
	background-color: lighten(whitesmoke,10%);
	box-shadow: @shadow;
	}

	&:checked {
	box-shadow: @shadow inset;
	cursor: initial;
	}
	}
	}