This is not a must hack. It is only for those who think it is neater to have the sidebar widget title set in the middle.
Centralize Blogger Gadget Title
This is what you do:
1. Log in to your Blogger account.
2. At the Dashboard, pull down the slider and click on "Theme".
3. Then click on the "Customize" button.
4. Next click on "Advanced".
5. Pull down the slider and click on "Add CSS". A box will appear next to it.
6. Now paste the code below in the empty box provided.
.section-columns h2, #sidebar-right-1 h2, #sidebar-left-1 {text-align: center;}
7. Finally click on "Apply to Blog" button.Now your Gadget title should be centralized.
REMINDER: Copy the code carefully. There is a dot in front of the code.
* Here is a post on how to centralize Blogger blog post title.