First, give this a read: http://practicaltypography.com/

I like your design. I just have a few nitpicks...

* Only center titles; don't center body text!

* Your body text should be 90 characters wide, max. The paragraph under the photo is much too wide.

* Spacing under titles seems too small to my eyes.

* Triangles as bullet points look a little odd (this is really subjective)

* The login button is in a bit of a weird place. Right-aligned is nice, but it looks misaligned vertically with the logo.

My take on this stylesheet would be...

    .headline { margin-top: 0; }
    .h1, h2, h3 { margin-top: 0.7em; margin-bottom: 0.7em; }

Remove text-center from any body copy. Use <ul> tags for lists.

Regardless of the above, your work looks great.