Answer 1

You can include CSS in <style> tag and JS in <script> tag. VS Code automatically identifies the three languages and adjusts

Answer 2

You can follow Taranjeet advice. Also note that the feature you are looking for exists in Adobe Brackets. With Brackets when you place the cursor on a tag or attribute in html and type ctrl+E it shows the css for that selector in the same tab

Answer 3

Use VS Code or NetBeans. Both will help you to do this soru_love 🙂