how to center a widgets in sidebar?

That’s a Css Problem…
What about posting the url or the code (style.css and sidebar.php)??

this is offline page
yes, i would like to know what i need to add/change to my style.css
or sidebar.php

Until you don’t post the code, i am not able to solve the problem definitely.. So try to add the tag <center> and </center> where there is the code that displays the image in sidebar.php…
Or try a better solution by editing the css in the class used by the image: add text-align:centre;

The best way to align elements is to use a fixed width (which must be less than the enclosing element) and then set the left and right margins to “auto”.

So if your widget has id=widget1 and is 300px wide, your CSS would be:

#widget1 {
margin: 0 auto;
}

The zero in the above (for top and bottom) can be whatever space you want.

See this for more: https://www.w3schools.com/css/css_align.asp

That rarely works in my experience…if it’s a text widget add margin-left or margin-right as an inline style – depending on what side of the page the sidebar is on. And yes, without a live site, we are only guessing.