Here is a fix that might work.
In the section that has:
/*
Resize images to fit the main content area.
- Applies only to images uploaded via WordPress by targeting size-* classes.
- Other images will be left alone. Use "size-auto" class to apply to other images.
*/
img.size-auto,
img.size-full,
img.size-large,
img.size-medium,
img.aligncenter,
.attachment img,
.widget-area img,
.wp-caption {
max-width: 100%; /* When images are too wide for containing element, force them to fit. */
height: auto; /* Override height to match resized width for correct aspect ratio. */
}
Hit return after the line with “/* Override height to match resized width for correct aspect ratio. */” and add this code:
display:block;
margin-left:auto;
margin-right:auto;
The code should now look like this:
/*
Resize images to fit the main content area.
- Applies only to images uploaded via WordPress by targeting size-* classes.
- Other images will be left alone. Use "size-auto" class to apply to other images.
*/
img.size-auto,
img.size-full,
img.size-large,
img.size-medium,
img.aligncenter,
.attachment img,
.widget-area img,
.wp-caption {
max-width: 100%; /* When images are too wide for containing element, force them to fit. */
height: auto; /* Override height to match resized width for correct aspect ratio. */
display:block;
margin-left:auto;
margin-right:auto;
}
Make sure that the last brace is still there.
That should hopefully work!