<main id="main">
	<form id="calc_form">
		<header class="calc_header">
			<input type="text" disabled id="output" class="calc_output" value="0" />
		</header>
		<footer class="calc_footer">
			<div class="btn_group">
				<button data-type="clear" type="reset" value="clear" class="btn btn-grey">
					AC
				</button>
				<button data-type="operator" value="invert" class="btn btn-grey">
					+/-
				</button>
				<button data-type="operator" value="%" class="btn btn-grey">
					%
				</button>
				<button data-type="operator" value="/" class="btn btn-orange">
					÷
				</button>
			</div>
			<div class="btn_group">
				<button data-type="operand" value="7" class="btn btn-dark-grey" id="7">
					7
				</button>
				<button data-type="operand" value="8" class="btn btn-dark-grey">
					8
				</button>
				<button data-type="operand" value="9" class="btn btn-dark-grey">
					9
				</button>
				<button data-type="operator" value="*" class="btn btn-orange">
					x
				</button>
			</div>
			<div class="btn_group">
				<button data-type="operand" value="4" class="btn btn-dark-grey">
					4
				</button>
				<button data-type="operand" value="5" class="btn btn-dark-grey">
					5
				</button>
				<button data-type="operand" value="6" class="btn btn-dark-grey">
					6
				</button>
				<button data-type="operator" value="-" class="btn btn-orange">
					-
				</button>
			</div>
			<div class="btn_group">
				<button data-type="operand" value="1" class="btn btn-dark-grey">
					1
				</button>
				<button data-type="operand" value="2" class="btn btn-dark-grey">
					2
				</button>
				<button data-type="operand" value="3" class="btn btn-dark-grey">
					3
				</button>
				<button data-type="operator" value="+" class="btn btn-orange">
					+
				</button>
			</div>
			<div class="btn_group">
				<button data-type="operand" value="0" class="btn btn-grow btn-dark-grey">
					0
				</button>
				<button data-type="operand" value="." class="btn btn-dark-grey">
					.
				</button>
				<button value="=" data-type="operator" class="btn btn-orange">
					=
				</button>
			</div>
		</footer>
	</form>
</main>

*,
*::after,
*::before {
	padding: 0px;
	margin: 0px;
	font-family: inherit;
}

body {
	background-color: #333333;
	display: flex;
	align-items: center;
	justify-content: center;
	font-size: 16px;
}

body,
html {
	height: 100vh;
	font-family: sans-serif;
}

button {
	cursor: pointer;
	border: 0px;
}

input[type="text"] {
	background-color: transparent;
	text-align: end;
	width: 100%;
	color: #d2d2d2;
	border: 0px;
	font-size: 4rem;
}

#main {
	border: 2px solid #ededed;
	border-radius: 50px;
	width: 100%;
	max-width: 280px;
	background-color: #000000;
	padding: 2rem 1rem;
}

.calc_header {
	margin-top: 90px;
	padding: 12px;
}

.calc_footer > * + * {
	margin-top: 1rem;
}

.calc_footer > *:last-child {
	gap: 1rem;
}

.btn_group {
	display: flex;
	justify-content: space-between;
	align-items: center;
	gap: 0.3rem;
}

.btn {
	display: flex;
	justify-content: center;
	align-items: center;
	border-radius: 50%;
	width: 60px;
	height: 60px;
	color: #ffffff;
	font-size: 20px;
	transition: all 0.3s cubic-bezier(0.19, 1, 0.22, 1);
}

.btn.btn-grow {
	flex-grow: 1;
	border-radius: 40px;
}

.btn:hover {
	transform: translate(-2px, -3px);
}

.btn.active {
	background-color: #ffffff;
	color: #f69906;
}

.btn-grey {
	background-color: #9f9f9f;
	color: #000;
}

.btn-grey:hover {
	background-color: #ededed;
}

.btn-dark-grey {
	background-color: #313131;
}

.btn-dark-grey:hover {
	background-color: #999999;
}

.btn-orange {
	background-color: #f69906;
}

.btn-orange:hover {
	background-color: orange;
}