site.css

.site-header {
    -webkit-border-top-left-radius: 8px;
    -moz-border-radius-topleft: 8px;
    border-top-left-radius: 8px;
    -webkit-border-top-right-radius: 8px;
    -moz-border-radius-topright: 8px;
    border-top-right-radius: 8px;
}

.icon-collapse:before {
    content: "\25BC";
    font-size: 15px;
    line-height: 12px;
}

.collapsed .icon-collapse:before {
    content: "\25B6";
}