Gallery CSS Problem

You have to account for all appropriate CSS classes, based on the number of columns passed to the shortcode. Here’s my CSS (borrowed heavily from Michael Fields), for handling from 1 to 10 columns:

.gallery {
    margin: 0px auto;
    text-align: center;
    width: 100%;
    min-width: 100%;
}
.gallery .gallery-item {
    float: left;
    margin: 0px auto;
    text-align: center;
}
.gallery img {
    border: 1px solid #cfcfcf;
}
.gallery .gallery-caption {
    display: none;
}
.gallery-columns-1 .gallery-item {
    max-width: 638px;
    width: 638px;
}
.gallery-columns-1 .gallery-item img { 
    max-width: 600px;
    height: auto;
    max-height: 600px;
}
.gallery-columns-2 .gallery-item {
    max-width: 300px;
    width: 300px;
}
.gallery-columns-2 .gallery-item img { 
    max-width: 300px;
    height: auto;
    max-height: 300px;
}
.gallery-columns-3 .gallery-item {
    max-width: 200px;
    width: 200px;
}
.gallery-columns-3 .gallery-item img { 
    max-width: 200px;
    height: auto;
    max-height: 200px;
}
.gallery-columns-4 .gallery-item {
    max-width: 151px;
    width: 151px;
}
.gallery-columns-4 .gallery-item img { 
    max-width: 150px;
    height: auto;
    max-height: 150px;
}
.gallery-columns-5 .gallery-item {
    max-width: 120px;
    width: 120px;
}
.gallery-columns-5 .gallery-item img { 
    max-width: 120px;
    height: auto;
    max-height: 120px;
}
.gallery-columns-6 .gallery-item {
    max-width: 100px;
    width: 100px;
}
.gallery-columns-6 .gallery-item img { 
    max-width: 100px;
    height: auto;
    max-height: 100px;
}
.gallery-columns-7 .gallery-item {
    max-width: 85px;
    width: 85px;
}
.gallery-columns-7 .gallery-item img { 
    max-width: 85px;
    height: auto;
    max-height: 85px;
}
.gallery-columns-8 .gallery-item {
    max-width: 75px;
    width: 75px;
}
.gallery-columns-8 .gallery-item img { 
    max-width: 75px;
    height: auto;
    max-height: 75px;
}
.gallery-columns-9 .gallery-item {
    max-width: 67px;
    width: 67px;
}
.gallery-columns-9 .gallery-item img { 
    max-width: 67px;
    height: auto;
    max-height: 67px;
}
.gallery-columns-10 .gallery-item {
    max-width: 60px;
    width: 60px;
}
.gallery-columns-10 .gallery-item img { 
    max-width: 60px;
    height: auto;
    max-height: 60px;
}

EDIT

Here you can see an example of the markup and styles being applied, from calling the following in the Post Content: