--- a
+++ b/v3/css/derived.css
@@ -0,0 +1,31 @@
+html {
+  box-sizing: border-box;
+}
+*, *:before, *:after {
+  box-sizing: inherit;
+}
+
+body {
+  margin: 0;
+  height: 100vh;
+  overflow: hidden;
+}
+
+.top-nav {
+  height: 40px;
+  border-bottom: 1px solid #eee;
+  padding: 5px;
+}
+
+.main-area {
+  position: absolute;
+  top: 40px;
+  bottom: 0;
+  left: 0;
+  width: 100vw;
+}
+
+.viewer-container {
+  width: 100%;
+  height: 100%;
+}