some changes

server.js

 	let tmpf = tmp.fileSync({ postfix: ".pdf" });
 
 	let child = spawn("pandoc",
-		[ "--standalone", "--pdf-engine=pdflatex", "--output", tmpf.name ]);
+		[ "--standalone", "--output", tmpf.name ]);
 
 	child.on("error", err => {
 		res.writeHead(500);
-		res.end(err);
+		res.end(JSON.stringify({ output: err.toString() }));
 		tmpf.removeCallback();
 	});
 

web/index.html

 					<canvas id="preview"></canvas>
 				</div>
 			</div>
-			<div id="pandoc-output">
-				Test
-			</div>
+			<div id="pandoc-output"></div>
 		</div>
 
 		<script src="https://cdn.jsdelivr.net/simplemde/latest/simplemde.min.js"></script>

web/style.css

 	grid-template-rows: auto 100px;
 	grid-template-areas:
 		'left-pane right-pane'
-		'footer footer';
+		'footer right-pane';
 }
 
 #editor-container {
 	overflow: auto;
 }
 
+#preview-controls {
+	line-height: 50px;
+}
+
 #pandoc-output {
 	grid-area: footer;
+	min-height: 0px;
+	white-space: pre;
+	overflow: auto;
 }