How to center title of a post on my website on CSS?

The title and image of my posts are not aligned with the rest of the website. I unfortunately had to tweak the menu and content a little bit to visually center it on the browser window, but it seems it might have created a 'shift' with the header/image.

example of post with the issue: http://www.overfit-not.com/the-danger-of-feature-selection-with-random-forests/

I have not been able to do this myself. Below is the code I used to actually center the content of the post relative to the menu.

.site-content {
    width: 105%;
    display: inline-block;
}