This will be accomplished with CSS styles. Could you give me a specific URL to look at and tell me where the buttons are? It'll be easier to inspect in the browser's developer tools to suggest styles if I can see your page/existing template styles.
[Edited to add]
Try code like this:
.sourcecoast.login .row-fluid {
width: 50%;
margin: 0 auto;
}
If that doesn't work seeing it in the browser is my next step.
-Melissa