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HTML

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CSS

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <h1>Larger Flexbox Form</h1>
<form class="cs-form cs-message">

    <label for="first-name">First Name: </label>
    <input type="text" class="field field1" placeholder="First Name" name="first-name" id="first-name">

    <label for="last-name">Last Name: </label>
    <input type="text" class="field field2" placeholder="Last Name" name="last-name" id="last-name">

    <label for="zip-code">Zip Code: </label>
    <input type="text" class="field field3" placeholder="Zip Code" name="zip-code" id="zip-code">

    <label for="spirit-animal">Spirit Animal: </label>
    <input type="text" class="field field4" placeholder="Spirit Animal" name="spirit-animal" id="spirit-animal">

    <label for="lottery">What will you do with your lottery winnings? </label>
    <textarea class="textarea" rows="5" cols="20" placeholder="What will you do with your lottery winnings?" name="lottery" id="lottery"></textarea>

    <button class="button" type="submit">
        OK
    </button>

</form>
!

CSS 

              
                $color-primary: #458599;

body {
	padding: 2%;
	color: #444;
	max-width: 980px;
	margin: 0 auto;
	background-color: #eaeaea;
}

label {
	position: absolute;
  clip: rect(1px 1px 1px 1px); 
  clip: rect(1px, 1px, 1px, 1px);
}
form {
	display: flex;
	flex-flow: row wrap;
}
.field, .textarea {
	margin: 0 .5em 1em 0;
	padding: .5em 1em;
	border: 1px solid #CCC;
}
.field {
	flex: 1 0 40%; //flex magic
	width: 45%;
	float: left;
}
.textarea {
	flex: 1 0 90%;
	width: 90%;
}
.button {
	padding: .5em 1em;
	border: 1px solid #CCC;
	background-color: $color-primary;
	color: #FFF;
}
!

JS 

              
                /*

Based on talk by Zoe Gillenwater at CSSconf 2015 https://www.youtube.com/watch?v=_98SE8WUvLk

http://www.slideshare.net/zomigi/enhancing-responsiveness-with-flexbox-css-conf-eu-2015

*/
!
999px

Console