Centering Header Image

.header-image {
    text-align: center;
    margin: 0 auto;
}

add this to bottom of your themes style.css

Don’t edit the theme files directly, otherwise your changes will be overwritten whenever the theme is updated.

An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS.

As alternatives, you could either install a standalone custom CSS plugin, or create a child theme.