there is nothing 'default styles' - these are styled within style.css of your theme, about in the middle:

`/* Pagination -------------- */

.pagination{
    background:#fff;
    width:618px;
    margin:0 0 0 1px;
}

.wp-pagenavi{
    padding:30px 25px 30px 25px;
    float:left;
}


.pagination span{
    float:left;
    display:block;
    font-family:Georgia, "Times New Roman", Times, serif;
    font-style:italic;
    font-size:12px;
    color:#666666;
    padding:3px 20px 0 0;
}

.pagination a, .wp-pagenavi .current{
    display:block;
    float:left;
    padding:3px 9px 2px 9px;
    border:1px solid #c6c6c6;
    color:#999;
    -webkit-box-shadow: 0px 0px 4px rgba(0, 0, 0, 0.1);
    -moz-box-shadow: 0px 0px 4px rgba(0, 0, 0, 0.1);
    margin:0 6px 0 0;
}

.pagination a:hover{
    border:1px solid #999;
    color:#444444;
}
`

and right at the end:

`/****** Pagenavi ********/
.wp-pagenavi {
    clear: both;
}

.wp-pagenavi a, .wp-pagenavi span {
    text-decoration: none;
    border: 1px solid #BFBFBF;
    padding: 3px 5px;
    margin: 2px;
}

.wp-pagenavi a:hover, .wp-pagenavi span.current {
    border-color: #000;
}

.wp-pagenavi span.current {
    font-weight: bold;
}`