For your second query, your buttons are in a text widget. I think you have two choices here. If you want the content of all text widgets to be 'centered', you can add style rules for the 'text-widget' class. If you only want this particular text widget to be affected, you'll need to change the style rules that someone (you? your developer?) have created for this text widget, in the text widget's HTML in your site's Dashboard.
Either way, I don't think you can really center the buttons. That would normally be done by giving them a fixed width and setting left and right margins to 'auto'. In this case, it's probably easier just to offset them from the left using a fixed margin. Although the former might be doable in the text widget's HTML.
Again, I'm not sure that this is going to be 'simple' enough for you. For all the questions you're asking, you need at least to know a bit about how WP themes work and how to alter the relevant CSS rules.
Cheers
PAE