Reorganized file structure

Moved app.css and index.css into the css folder.

client/src/css/App.css

@@ -0,0 +1,6 @@
+#root {
+  max-width: 1280px;
+  margin: 0 auto;
+  padding: 2rem;
+  text-align: center;
+}

client/src/css/index.css

@@ -0,0 +1,4 @@
+:root {
+  font-family: Georgia, 'Times New Roman', Times, serif;
+  color: #19332D;
+}