wpbits

Custom CSS for Blocks allows you to easily write custom CSS for any block or post on your WordPress website, giving you complete control over the design of your content. You can take advantage of SASS support to write clean, efficient code. And, with optimized inline output on demand, you can ensure that your website loads quickly and efficiently for your visitors.

Custom CSS for Blocks

Bytes.co

Harness the power of pre-processed CSS and minified JS in your theme or plugin, without any complicated installs or build tools. Simply tell WP Compiler where to find your source files and where to put the compiled results, then throw your install into Dev Mode. WP Compiler watches your source folders for you, and recompiles your CSS and JS on any file change. WP Compiler supports both SCSS and LESS precompilers for CSS, to suit anyone’s preference.
When you’re ready to launch a new site, just turn off Dev Mode, and your styles and javascript will be compiled & minimized and comments & source maps will be removed. With Dev mode disabled, Compiler will stop watching source directories, so there is no effect on site performance, but you can still apply a quick change at any time, by clicking the compile button in the admin toolbar.
WP Compiler relies on <a href="http://leafo.github.io/scssphp/" rel="nofollow ugc">scssphp</a>, <a href="http://lessphp.typesettercms.com/" rel="nofollow ugc">lessphp</a>, and <a href="https://www.minifier.org/" rel="nofollow ugc">minify</a>. 
Specific issues with the underlying compilation libraries should be submitted to their respective developers.

WP Compiler

Harness the power of pre-processed CSS and minified JS in your theme or plugin, without any complicated installs or build tools.

Custom CSS for Blocks vs WP Compiler