src/Pure_CSS_Gallery.php
public function _tiny_mce_before_init( $mce_init ) {
		$styles  = '#tinymce .wpview .gallery { margin: 0; display: block; border: 2px solid #666; text-align: center; height: 80px; }';
		$styles .= '#tinymce .wpview .gallery > * { display: none; }';
		$styles .= '#tinymce .wpview .gallery::before { margin-top: 20px; display: inline-block; content: \'\\\\f161\'; font-family: dashicons; font-size: 18px; color: #666 }';
		if ( isset( $mce_init['content_style'] ) ) {
			$mce_init['content_style'] .= $styles;
		} else {
			$mce_init['content_style'] = $styles;
		}
		return $mce_init;
	}
public function _tiny_mce_before_init( $mce_init ) {
		$styles  = '#tinymce .wpview .gallery { margin: 0; display: block; border: 2px solid #666; text-align: center; height: 80px; }';
		$styles .= '#tinymce .wpview .gallery > * { display: none; }';
		$styles .= '#tinymce .wpview .gallery::before { margin-top: 20px; display: inline-block; content: \'\\\\f161\'; font-family: dashicons; font-size: 18px; color: #666 }';
		if ( isset( $mce_init['content_style'] ) ) {
			$mce_init['content_style'] .= $styles;
		} else {
			$mce_init['content_style'] = $styles;
		}
		return $mce_init;
	}
public function _tiny_mce_before_init ( $ mce_init ) { $ styles = '#tinymce .wpview .gallery { margin: 0; display: block; border: 2px solid #666; text-align: center; height: 80px; }' ; $ styles .= '#tinymce .wpview .gallery > * { display: none; }' ; $ styles .= '#tinymce .wpview .gallery::before { margin-top: 20px; display: inline-block; content: \'\\\\f161\'; font-family: dashicons; font-size: 18px; color: #666 }' ; if ( isset ( $ mce_init [ 'content_style' ] ) ) { $ mce_init [ 'content_style' ] .= $ styles ; } else { $ mce_init [ 'content_style' ] = $ styles ; } return $ mce_init ; }
Change style of gallery in wysiwyg

@param array $mce_init
Change style of gallery in wysiwyg