.parent {
	margin: 10px auto;
	display: grid;
	grid-template-rows: 50px 1fr;
	grid-template-columns: 300px 1fr;
	grid-template-areas: 
		"input input " 
		"first second ";
}

.input {
	grid-area: input;
}

.first {
	grid-area: first;
	margin: 10px;
}

.second {
	grid-area: second;
	margin: 10px;
}

.imagebox {
	border: 1px solid green;
	box-sizing: border-box;
	height: 400px;
	width: 100%;
	overflow: auto;
	text-align: center;
}

#output {
	box-sizing: border-box;
	min-height: 400px;
	width: 100%;
	resize: none;
}