* {
	box-sizing: border-box;
	margin: 0;
	padding: 0;
	font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
}

body {
	display: flex;
	justify-content: center;
	align-items: center;
	min-height: 100vh;
	background: linear-gradient(135deg, #141e30, #243b55);
}

.calculator {
	background-color: #1e293b;
	padding: 24px;
	border-radius: 20px;
	box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
	width: 350px;
}

.screen {
	background-color: #0f172a;
	padding: 20px;
	border-radius: 12px;
	text-align: right;
	margin-bottom: 20px;
	min-height: 100px;
	display: flex;
	flex-direction: column;
	justify-content: space-between;
	word-break: break-all;
}

.preview {
	color: #94a3b8;
	font-size: 1.1rem;
	min-height: 1.5rem;
}

.display {
	color: #ffffff;
	font-size: 2.5rem;
	font-weight: 600;
	overflow-x: auto;
}

.buttons {
	display: grid;
	grid-template-columns: repeat(4, 1fr);
	gap: 12px;
}

button {
	padding: 20px;
	border: none;
	border-radius: 12px;
	font-size: 1.5rem;
	font-weight: 600;
	cursor: pointer;
	transition: all 0.1s ease;
	background-color: #334155;
	color: #f8fafc;
}

button:hover {
	background-color: #475569;
	transform: translateY(-2px);
}

/* Mouse click and Keyboard trigger visual effect */
button:active,
button.kbd-active {
	transform: scale(0.95) !important;
	background-color: #64748b !important;
	box-shadow: inset 0 4px 6px rgba(0, 0, 0, 0.4);
}

button.operator {
	background-color: #f59e0b;
	color: #ffffff;
}

button.operator:hover {
	background-color: #d97706;
}

button.operator.kbd-active {
	background-color: #b45309 !important;
}

button.clear {
	background-color: #ef4444;
	color: #ffffff;
	grid-column: span 2;
}

button.clear:hover {
	background-color: #dc2626;
}

button.clear.kbd-active {
	background-color: #b91c1c !important;
}

button.equal {
	background-color: #10b981;
	color: #ffffff;
	grid-column: span 2;
}

button.equal:hover {
	background-color: #059669;
}

button.equal.kbd-active {
	background-color: #047857 !important;
}

button.zero {
	grid-column: span 2;
}