The new Gutenberg editor provided by WordPress is pretty neat. However, there are certain limits of the ability to align text as what we usually do in Microsoft Word, especially the nice-looking “justified text”.
In earlier version of the editor, we can open the extended editing bar and there would be a Justified Alignment option to click and apply on the paragraph. The current one doesn’t have it. To resolve this problem, there are several options: install the old editor plugin (which will be supported till 2022), or simply put the CSS code in the Additonal CSS section of the current theme setting:
Then all the paragraphs from now on will be formatted as Justified.