This theme comes with a built-in tweak for the Concrete5 Login block ( Simply put the block in the "Header" section, and it'll "flatten out" and theme it. You can then position it in the top right-hand corner (see the demo site) by using this CSS:

position: absolute;
top: 0px;
right: 0px;

You can also use the CSS class content_box to put a green box around any content. Perfect for making items really stand out!