(blog) 100days challenge 14 (#22799)

* Add use themes blog post

* chore: format

* Fix typos

Co-authored-by: gatsbybot <[email protected]>

docs/blog/100days/use-themes/index.md

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+---
+title: Challenge 14 - Rapidly Build Sites with Gatsby Themes
+date: 2020-04-03
+author: "Hashim Warren"
+excerpt: "Learn how to use a Gatsby Theme in your project"
+tags: ["learning-to-code", "100-Days-of-Gatsby"]
+---
+
+_Gatsby was named the [#1 new technology to learn in 2020](https://www.cnbc.com/2019/12/02/10-hottest-tech-skills-that-could-pay-off-most-in-2020-says-new-report.html)!_
+
+_To help you learn about Gatsby and our ecosystem, we invite you to take the #100DaysOfGatsby challenge! If you are new to Gatsby, you can follow along with our beginner-friendly weekly prompts. Or if you are familiar with Gatsby and want to go deeper, we invite you to [build your first Gatsby Theme](/docs/themes/building-themes/)._
+
+_Learn more about [#100DaysOfGatsby here](/blog/100days)!_
+
+## Challenge 14: Spin Up a New Site with a Gatsby Theme
+
+For the final two challenges you will explore using and creating Gatsby Themes!
+
+So far you’ve created a Gatsby site from scratch, and added features for usage on a single site. Gatsby Themes opens up the possibility to leverage good ideas from the Gatsby ecosystem, and share your own configurations and designs. You can think of Gatsby Themes as handy website kits that can be shared, customized, and stacked together.
+
+Before you dive into creating a theme, our resources below will point you to the philosophy behind Gatsby Themes and common use cases. Then we’ll show you how to use a theme in your poject. And next week you'll explore creating your own theme!
+
+### Gatsby Theme Usage Resources
+
+#### Theme Philosophy
+
+[Why Gatsby Themes](/blog/2019-01-31-why-themes) Kyle Mathews gives a short intro into Gatsby Themes, and why this functionality was added to Gatsby
+
+[What are Gatsby Themes](https://youtu.be/LBpNwUU3QVI) Chris Biscardi presents a high level view of how themes work in Gatsby
+
+[Using Theme for Distributed Docs](/blog/2019-07-03-using-themes-for-distributed-docs/) The Apollo team explains how and why they use Gatsby Themes
+
+#### Theme Usage
+
+[Discover a Gatsby Theme](/plugins/?=gatsby-theme) Browse Gatsby’s plugin repository to find the right theme for your project
+
+[Use a Gatsby Theme](/docs/themes/using-a-gatsby-theme/) Step-by-step guide to the conventions of Gatsby Theme usage (hint: "shadow and extend", don’t fork 🙂 )
+
+### What to Do If You Need Help
+
+If you get stuck during the challenge, you can ask for help from the [Gatsby community](/contributing/community/) and the [ASKGatsbyJS](https://twitter.com/AskGatsbyJS) Twitter account. You can find fellow Gatsby Developers on [Discord](https://discordapp.com/invite/gatsby), [Reddit](https://www.reddit.com/r/gatsbyjs/), [Spectrum](https://spectrum.chat/gatsby-js), and [Dev](https://dev.to/t/gatsby).