The default, ‘plain vanilla’ WordPress text widget sorely lacks functionalities and requires HTML knowledge if you want to do anything beyond the barest functionality it provides – even like changing a font color!
I found the Black Studio TinyMCE Widget early on in my WordPress career – and what a find it is! This plugin adds a Visual Editor widget that allows you to insert rich text and media objects in your sidebars with no hassle and no need to know code. With Black Studio TinyMCE Widget you will be able to edit in a WYSIWYG manner using the native WordPress TinyMCE editor, just like you do in posts and pages. And, if you are a developer, you can still switch back and forth from Visual to Text (HTML) mode.
To learn more, visit the Black Studio TinyMCE Widget write-up on wordpress.org.