Hi there, I’ll answer your questions separately.
1) how do i change the button graphic in the theme?
To change the button graphic you’ll need to target the image path on each element where it’s used. You can use a browser inspector to help find the right elements to target.
For example, on widget titles, this is the element you’d need to target:
.widget-title::before {
background: rgba(0, 0, 0, 0) url("https://your/image/path/image.svg") no-repeat scroll 0 0 / 84px 22px;
}
Replace the fake image path with your own. Button uses an SVG image for most flexibility. If you’d like do to the same, note that SVGs can’t currently be uploaded in the WordPress media library so you’ll need to use FTP.
Don’t edit the theme files directly, otherwise your changes will be overwritten every time the theme is updated to the latest version.
Since you’re already using Jetpack, an easy way to add custom CSS is to 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.