style.css

/******************************************************************************/
/* Built-in Elements                                                          */
/******************************************************************************/

* {
	box-sizing: border-box;
	margin: 0;
	padding: 0;
	font-family: monospace;
	font-size: 1em;
}

html, body {
	min-width: 200px;
}

h1 {
	font-size: 2em;
}

fieldset {
	position: relative;
	border: none;
}

legend {
	margin-bottom: 8px;
	font-weight: bold;
}

legend::after {
	content: ":";
}

input[type="text"] {
	padding: 4px;
	border: 1px solid #737373;
}

button {
	padding: 8px 16px;
}

textarea {
	width: 100%;
	height: 100px;
	padding: 4px;
}

/******************************************************************************/
/* Page Sections                                                              */
/******************************************************************************/

#header {
	padding: 32px;
	text-align: center;
}

#error {
	margin-bottom: 16px;
	padding: 4px;
	text-align: center;
	color: #eb400c;
}

#content {
	padding: 16px;
	border-top: 1px solid #000000;
	border-bottom: 1px solid #000000;
	background-color: #dddddd;
}

#footer {
	padding: 16px;
	text-align: center;
}

/******************************************************************************/
/* Content Sections                                                           */
/******************************************************************************/

.result, .regex, .modifiers {
	margin-top: 24px;
	margin-bottom: 24px;
}

.documentation li {
	display: inline-block;
	margin-right: 24px;
}

.result {
	padding: 16px;
	border: 1px solid #737373;
	background-color: #ffffff;
	white-space: pre-wrap;
	word-wrap: break-word;
}

.result mark {
	background-color: #f9d3d3;
}

.regex label {
	display: block;
	margin-bottom: 2px;
	font-weight: bold;
}

.regex label::after {
	content: ":";
}

.regex textarea + label, .regex input + label {
	margin-top: 8px;
}

.modifiers .modifier {
	display: block;
	margin-bottom: 4px;
}

.modifiers .modifier input[type="checkbox"] {
	float: left;
}

.modifiers .modifier label {
	display: block;
	margin-left: 24px;
}

.actions button {
	width: 100%;
}

.actions button + button {
	margin-top: 12px;
}

@media (min-width: 481px) {
	.actions button {
		width: auto;
		margin-right: 12px;
	}

	.actions button + button {
		margin-top: 0;
	}
}