kyarauk Thanks for posting your solution!
For anyone else reading this, rather than adding inline CSS to each image, adding a bit of custom CSS is a better solution. The specific code would depend on which ID is assigned to your particular text widget, but it would look like what I provided to becomingsupersonic above.
but the free version, so no access to the style sheet for the theme.
Forever is a free theme, there is no paid version. It sounds like you may be on WordPress.com, though – it has separate forums, in case you need help in the future. (These forums are for folks running WordPress on their own hosting.)
https://en.forums.wordpress.com/
Here are some tips on getting help in the WordPress.com forums: https://en.support.wordpress.com/getting-help-in-the-forums/