.aligncenter,
div.aligncenter {
   display: block;
   margin-left: auto;
   margin-right: auto;
}

.alignleft {
   float: left;
}

.alignright {
   float: right;
}

.wp-caption {
   border: 1px solid #ddd;
   text-align: center;
   background-color: #f3f3f3;
   padding-top: 4px;
   margin: 10px;
   /* optional rounded corners for browsers that support it */
   -moz-border-radius: 3px;
   -khtml-border-radius: 3px;
   -webkit-border-radius: 3px;
   border-radius: 3px;
}

.wp-caption img {
   margin: 0;
   padding: 0;
   border: 0 none;
}

.wp-caption p.wp-caption-text {
   font-size: 11px;
   line-height: 17px;
   padding: 0 4px 5px;
   margin: 0;
}
.categories {...}
.cat-item {...}
.current-cat {...}
.current-cat-parent {...}
.pagenav {...}
.page_item {...}
.current_page_item {...}
.current_page_parent {...}
.widget {...}
.widget_text {...}
.blogroll {...}
.linkcat{...}

http://codex.wordpress.org/CSS

Standard CSS markup for wordpress

Required CSS for wordpress

css, wordpress

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