[Pro Sites] Select template preview image size about

I how to resize pro-site page select template preview image resize ?

.theme-previewer-wrap,

.theme-page-showcase-wrap,

.theme-screenshot-wrap {

width:45%;

float:left;

margin-right: 13px;

margin-bottom:25px;

box-sizing:border-box;

position:relative;

padding:3px;

max-width:600px;

}

______________

.theme-previewer-wrap,

.theme-page-showcase-wrap,

.theme-screenshot-wrap {

width:45%;

float:left;

margin-right: 13px;

margin-bottom:25px;

box-sizing:border-box;

position:relative;

padding:3px;

max-width:600px;

}

This code dont working