Make Header Image Responsive (resize)

Remove this code:

#logo img { max-width:964px; }

There is no such code in the php file. I could find the following code in the style.css file:
#logo img {
height: auto;
max-width: 100%;
}

The logo image is responsive, the max width and height setting makes it responsive. This might help you, https://4bzthemes.com/support/topic/logo-size-issue/, disregard the centering part.