Basic layout and categories nav

app/styles/_layout.scss

@@ -0,0 +1,46 @@
+* {
+  box-sizing: border-box;
+}
+
+#remotestorage-widget {
+  position: fixed;
+  top: 0.5rem;
+  right: 0.5rem;
+}
+
+#app-container {
+  position: absolute;
+  top: 0;
+  left: 0;
+  bottom: 0;
+  right: 0;
+  overflow: hidden;
+  display: flex;
+  flex-direction: row;
+  justify-content: flex-start;
+  align-items: stretch;
+
+  > aside {
+    flex: 0 0 16rem;
+    padding: 2rem;
+    overflow: auto;
+
+    nav {
+      ul {
+        list-style: none;
+        margin: 0;
+        padding: 0;
+      }
+      a {
+        display: block;
+        padding: 0.2rem 0;
+      }
+    }
+  }
+
+  > main {
+    flex: 1;
+    padding: 2rem;
+    overflow: auto;
+  }
+}