How to get Responsive logo picture

I have added my own logo from dashboard and also change the size in the function file to fit my picture.
width’ => 960, ‘height’ => 120
But. How can I do to make this header picture to be responsive?

I have try to add.

.header-image .site-title a {
float: left;
min-height: 110px;
width: 100%;
}

Under the @media only in CSS

Take a look at the site and please help me if you can.. http://lunchguidenpitea.se/