Mary Rose Elbambo

BlockGlow adds a “BlockGlow — Custom CSS” panel to the inspector of every block. Use it to scope custom CSS to a single block instance. The plugin stores CSS in the uploads folder (under uploads/blockglow/) and enqueues the generated CSS file when rendering on the front end. If the uploads directory isn’t writable or file write fails, BlockGlow will fall back to outputting inline styles.
Key features:
<ul>
<li>Adds two block attributes to every block: <code>blockglowCustomCSS</code> and <code>blockglowId</code>.</li>
<li>Inspector panel with a CodeMirror-backed code editor (if WordPress provides it) or a fallback textarea supporting Tab and Shift+Tab outdent.</li>
<li>Live preview inside the block editor: custom CSS is scoped to the block in the editor so you can see the effect while editing.</li>
<li>CSS files are saved to <code>wp-content/uploads/blockglow/blockglow-<id>.css</code> and enqueued on the front end as a linked stylesheet; files are removed automatically when you clear the Custom CSS field.</li>
<li>Graceful fallback to inline styles when file writing isn’t possible.</li>
</ul>
How scoping works:
BlockGlow creates a unique <code>blockglowId</code> for each block instance and scopes your CSS with a wrapper selector like:
<pre><code>[data-blockglow-id="bg-xxxxxxx"] { /* your declarations */ }
</code></pre>
For convenience you can use <code>&</code> as the wrapper shorthand in the editor. Example:
<pre><code>& .my-class { color: red; }
</code></pre>
The plugin will replace <code>&</code> with the wrapper selector for both editor preview and front-end output.
<h3>Support</h3>
If you find issues or want improvements (for example: limiting who can edit per-block CSS, collecting styles into a single head include, or adding an admin UI to manage generated CSS files), open an issue in the repository or reply here and I will assist.

BlockGlow — Per-block Custom CSS

Adds a "Custom CSS" inspector panel to every Gutenberg block and saves per-block CSS files to uploads for front-end enqueuing.

Ozan Canakli

This plugin allows you to add custom site-wide CSS, JavaScript, Header, Footer Code to your WordPress site. The changes appear instantly on your website with help of WordPress Live Customizer.
<iframe loading="lazy" class="youtube-player" width="750" height="422" src="https://www.youtube.com/embed/gP78wXPayvU?version=3&rel=1&showsearch=0&showinfo=1&iv_load_policy=1&fs=1&hl=en-US&autohide=2&wmode=transparent" allowfullscreen="true" style="border:0;" sandbox="allow-scripts allow-same-origin allow-popups allow-presentation allow-popups-to-escape-sandbox"></iframe>
In your WordPress Dashboard, navigate to Customize > Live Code Editor to get started.
When you Change or Update your WordPress Theme, Your Custom Code isn’t effected from these changes.
NEW FEATURES as Version 1.0.5: 
* Add Custom CSS to WordPress Admin dashboard. 
* Add Custom JavaScript to WordPress Admin dashboard.
MAIN FEATURES:
<ul>
<li>Custom CSS code</li>
<li>Custom Javascript code</li>
<li>Custom Header Code (Inside tags)(Google Analytics and Facebook Pixel compatible.)</li>
<li>Custom Footer Code (Before closing tag aka wp_footer function)</li>
<li>See Your Changes Immediately on your WordPress Site</li>
<li>Built in Syntax Code Highlighter</li>
<li>16 Color Schemes (Monokai, Chrome, GitHub, Twilight, Dreamweaver, XCode, Eclipse etc. 8 Light, 8 Dark)</li>
<li>Live Syntax Checking (CSS, JavaScript, HTML)</li>
<li>Syntax Highlighting</li>
<li>Line wrapping</li>
<li>Code folding</li>
<li>Multiple cursors and selections</li>
<li>Handles huge code blocks (four million lines seems to be the limit!)</li>
</ul>
Special thanks to <a href="https://profiles.wordpress.org/justinbusa/" rel="nofollow ugc">Justin Busa</a> of <a href="https://wordpress.org/plugins/beaver-builder-lite-version/" rel="ugc">Beaver Builder</a> for the inspiration.

Live Custom CSS JS Code Editor

Live Custom CSS JS Code Editor allows you to easily add custom CSS, JavaScript, Header, Footer Code to your site, straight from your WordPress Customi …

BlockGlow — Per-block Custom CSS vs Live Custom CSS JS Code Editor