body {
	margin: 0;
	font-size: 18px;
}
label {
	display: block;
	margin-bottom: 0.5em;
	font-size: 16px;
}
#calculator {
	max-width: 480px;
	margin: 0 auto;
	padding: 40px;
}
.value {
	margin-bottom: 1em;
}
button, input, select, textarea {
	font-size: 100%;
	margin: 0;
}
input {
	width: 100%;
	padding: .75em 1em;
	border: none;
	box-shadow: 0 0 0 2px rgba(0,0,0,.05);
	position: relative;
}
input:focus {
	outline: none;
	animation: shadow-animation 0.3s forwards;
}

@keyframes shadow-animation {
	0% { box-shadow: 0 0 0 2px rgba(0,0,0,.05); }
	70% { box-shadow: 0 0 0 8px rgba(0,0,0,.05); }
	100% { box-shadow:0 0 0 2px rgba(0,0,0,.05); }
}

button {
	width: 100%;
	padding: .75em 1em;
	margin-bottom: 1em;
	border: none;
	box-shadow: 0 0 0 2px rgba(0,0,0,.05);
}
#result {
	text-align: center;
	padding: 1em;
	opacity: 0;
	min-height: 30px;
	transition: opacity .2s;
}
#result.is-active {
	opacity: 1;
}
.forumula {
	text-align: center;
}