Add styling info to readme

Indent elements styles code example

README.md

@@ -102,12 +102,37 @@ gulp
 
 Build and optimize the current project, ready for deployment. This includes linting as well as vulcanization, image, script, stylesheet and HTML optimization and minification.
 
-## Application Theming
+## Application Theming & Styling
 
 Polymer 1.0 introduces a shim for CSS custom properties. We take advantage of this in `app/styles/app-theme.html` to provide theming for your application. You can also find our presets for Material Design breakpoints in this file.
 
 [Read more](https://www.polymer-project.org/1.0/docs/devguide/styling.html) about CSS custom properties.
 
+### Styling
+1. ***main.css*** - to define styles that can be applied outside of Polymer's custom CSS properties implementation. Some of the use-cases include defining styles that you want to be applied for a splash screen, styles for your application 'shell' before it gets upgraded using Polymer or critical style blocks that you want parsed before your elements are.
+2. ***app-theme.html*** - to provide theming for your application. You can also find our presets for Material Design breakpoints in this file.
+3. ***shared-styles.html*** - to shared styles between elements and index.html.
+4. ***element styles only*** - styles specific to element. These styles should be inside the `<style></style>` inside `template`.
+  ```html
+  <dom-module id="my-list">
+    <template>
+      <style>
+        :host {
+          display: block;
+          background-color: yellow;
+        }
+      </style>
+      <ul>
+        <template is="dom-repeat" items="{{items}}">
+          <li><span class="paper-font-body1">{{item}}</span></li>
+        </template>
+      </ul>
+    </template>
+  </dom-module>
+  ```
+
+These style files are located in the [styles folder](app/styles/).
+
 ## Unit Testing
 
 Web apps built with Polymer Starter Kit come configured with support for [Web Component Tester](https://github.com/Polymer/web-component-tester) - Polymer's preferred tool for authoring and running unit tests. This makes testing your element based applications a pleasant experience.

app/styles/shared-styles.html

@@ -1,4 +1,4 @@
-<!-- shared-styles.html -->
+<!-- shared styles for all elements and index.html -->
 <dom-module id="shared-styles">
   <template>
     <style>