Centering header image

I’ve been trying to figure out how to center my header image all day now. I’ve found solutions that worked for other people, but it seems that they’re all very theme specific.

My site is happieducks.com

I believe that the code I need to edit is somewhere in this:

/* Overall */
  .container {margin: 10px auto; width: 90%; overflow: hidden;}
  .header {position: relative; width: 90%; margin: 0 auto; padding: 40px 0 0 0;}
  .section {float: left; width: 60%; margin: 20px 0}
  .aside {float: right; width: 35%; margin: 30px 0; background: #fff; border-left: 2px solid #000;}
  .footer {clear: both; overflow: hidden; margin: 0 auto; width: 100%; color: #777;}

  /* .header form */
  .header-form {clear: both; overflow: hidden; position: absolute; top: 4px; right: 40px;}
  .header-text {width: 80px; border: 1px solid #fff;}

  /* .header */
  .header h1,
  .header h5 {font-size: 40px; text-transform: uppercase; margin: 10px 0 0 0;}
  .header-title {color: #888;}
  .header-desc {margin: 0; color: #777;}

EDIT:

Forgot to mention, my theme is a child theme of Adelle.