Polish styling, add row sum

assets/main.css

@@ -1,22 +1,28 @@
 /* App-wide styling */
+html, body, #main {
+	margin: 0;
+	padding: 0;
+	height: 100%;
+}
 body {
     background-color: #efeffc;
     color: #000000;
     font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
-    margin: 20px;
 }
 
 main {
   margin: auto;
   max-width: 40rem;
-  justify-content: center;
+  justify-content: space-between;
   display: flex;
   flex-direction: column;
+  height: 100%;
 }
 
 table {
     border-collapse: collapse;
     border-spacing: 0;
+	margin: 3rem 0;
 }
 
 tr {
@@ -26,6 +32,16 @@ tr {
 td {
     border: 1px solid gray;
     text-align: center;
+	padding: 2px;
+}
+
+#controls {
+	margin: 3rem 0;
+	display: flex;
+}
+
+#controls > * {
+	flex: 1 1 auto;
 }
 
 .number {