#customizer-wrapper { 
    width: 950px;
    height: 550px;
    padding: 0;
    text-align:center; 
    margin-left: auto;
    margin-right: auto;
}
body.mystyle-customize {
    min-width: 950px;
}

body.mystyle-customize .entry-content,
body.mystyle-customize article {
    max-width: none;
    min-width: 950px;
}

body.mystyle-customize .entry-header {
    min-width: 950px;
    margin-left: auto;
    margin-right: auto;
}

body.mystyle-customize #secondary,
body.mystyle-customize .site::before {
    display: none;
}
body.mystyle-customize .site-content {
    margin-left: auto;
}