chore: add inline codeblocks around some text for readability (#20720)

* Update post-css.md

* Update tailwind-css.md

* Update bulma.md

docs/docs/bulma.md

@@ -22,7 +22,7 @@ plugins: [`gatsby-plugin-sass`],
 
 Now is the time to create a scss-file that holds your simple style customisation and the import statement for bulma.
 
-(To keep things simple, insert the file next to index.js in the pages-directory)
+(To keep things simple, insert the file next to `index.js` in the pages-directory)
 
 ```scss:title=mystyles.scss
 @charset "utf-8";
@@ -37,7 +37,7 @@ $title-color: #ff0000;
 
 The last step is to import the style and use it.
 
-Replace the default contents of the index.js file.
+Replace the default contents of the `index.js` file.
 
 ```jsx:title=index.js
 import React from "react"

docs/docs/post-css.md

@@ -22,7 +22,7 @@ plugins: [`gatsby-plugin-postcss`],
 
 > **Note**: If you need to pass options to PostCSS use the plugins options; see [postcss-loader](https://github.com/postcss/postcss-loader) for all available options.
 
-3.  Write your stylesheets using PostCSS (.css files) and require or import them as normal.
+3.  Write your stylesheets using PostCSS (`.css` files) and require or import them as normal.
 
 ```css:title=styles.css
 @custom-media --med (width <= 50rem);

docs/docs/tailwind-css.md

@@ -50,7 +50,7 @@ plugins: [`gatsby-plugin-postcss`],
 
 3. Configure PostCSS to use Tailwind
 
-Create a postcss.config.js in your project's root folder with the following contents.
+Create a `postcss.config.js` in your project's root folder with the following contents.
 
 ```javascript:title=postcss.config.js
 module.exports = () => ({
@@ -89,7 +89,7 @@ npm install tailwindcss@0.7.4
 npm install tailwind.macro
 ```
 
-2. Use the Babel Macro (tailwind.macro) in your styled component
+2. Use the Babel Macro (`tailwind.macro`) in your styled component
 
 ```javascript
 import styled from "styled-components"