CSS tweak to content container (#66)

Prevents unneeded scrollbars, cleans up presentation a bit.

app/css/app.css

@@ -1,6 +1,7 @@
 
 html, body {
   height: 100%;
+  margin: 0px;
 }
 
 .hidden {
@@ -10,7 +11,7 @@ html, body {
 #container {
   display: flex;
   width: 100%;
-  height: 100%;
+  height: 100%; 
 }
 
 #modeler {
@@ -26,6 +27,19 @@ html, body {
   min-width: 400px;
 }
 
+/** 
+Remove the height of the header from the main content area,
+(prevents vertical scroll bars you don't need),
+adjust CSS props so that padding won't add to dimensions.
+*/
+#container:has(#modeler) {
+  -webkit-box-sizing: border-box; 
+  -moz-box-sizing: border-box;    
+  box-sizing: border-box;   
+  height: calc(100% - 65px);
+  padding: 8px;
+}
+
 .djs-label {
   font-family: 'Arial', sans-serif;
 }