inline-block-styles-cleanup.php

<?php

add_filter(
	'render_block',
	function( $html ) {
		static $styled_els = array();
		$styles_to_add     = '';

		// Find elements that have inline styles.
		preg_match_all( '/<[a-zA-Z0-9]+.+style=.+>/U', $html, $matches );

		// Loop elements.
		foreach ( $matches as $match ) {
			if ( empty( $match ) ) {
				continue;
			}

			foreach ( $match as $part ) {

				// Sanity check.
				if ( false !== strpos( $part, 'style=""' ) || false !== strpos( $part, "style=''" ) ) {
					continue;
				}

				// Get the styles.
				$styles             = preg_match( '/style=".+"|style=\'.+\'/', $part, $style_matches );
				$has_classes        = false !== strpos( $part, 'class="' );
				$class_names_to_add = array();
				$updated_el         = $part;

				// Loop styles.
				foreach ( $style_matches as $style_match ) {
					$styles_array = explode( ';', ltrim( ltrim( rtrim( $style_match, '"\'' ), 'style=' ), '"\'' ) );
					foreach ( $styles_array as $item ) {
						$item = trim( $item );

						// Skip complex styles.
						if ( false !== strpos( $item, '(' ) || false !== strpos( $item, '#' ) || false !== strpos( $item, '=' ) ) {
							continue;
						}

						// The classname.
						$class_name_to_add = trim( str_replace( array( ':', ' ' ), array( '-', '' ), $item ) );
						if ( empty( $class_name_to_add ) ) {
							continue;
						}

						// Build the CSS for this classname.
						$class_names_to_add[] = $class_name_to_add;
						if ( ! in_array( $class_name_to_add, $styled_els, true ) ) {
							$styled_els[]   = $class_name_to_add;
							$styles_to_add .= '.' . $class_name_to_add . '{' . $item . ';}';
						}

						// Remove inline styles.
						$updated_el = str_replace( array( " $item; ", "$item; ", " $item;", $item ), '', $part );
					}
				}

				if ( empty( $class_names_to_add ) ) {
					continue;
				}

				// Add classnames to the element.
				$updated_el = $has_classes
					? str_replace(
						array( 'class="', "class='" ),
						array( 'class="' . implode( ' ', $class_names_to_add ) . ' ', "class='" . implode( ' ', $class_names_to_add ) . ' ' ),
						$updated_el
					)
					: str_replace(
						'style=',
						'class="' . implode( ' ', $class_names_to_add ) . '" style=',
						$updated_el
					);

				$html = str_replace( $part, $updated_el, $html );
			}
		}

		// Append styles.
		if ( ! empty( $styles_to_add ) ) {
			$html .= "<style>$styles_to_add</style>";
		}

		return $html;
	}
);