in nettalk-ui.css :
/* Corner radius */
.nt-corner-tl { -moz-border-radius: 4px 0px 0px 0px; -webkit-border-radius: 4px 0px 0px 0px; border-radius: 4px 0px 0px 0px; behavior: url(PIE.htc);}
.nt-corner-tr { -moz-border-radius: 0px 4px 0px 0px; -webkit-border-radius: 0px 4px 0px 0px; border-radius: 0px 4px 0px 0px; behavior: url(PIE.htc);}
.nt-corner-bl { -moz-border-radius: 0px 0px 4px 0px; -webkit-border-radius: 0px 0px 4px 0px; border-radius: 0px 0px 4px 0px; behavior: url(PIE.htc);}
.nt-corner-br { -moz-border-radius: 0px 0px 0px 4px; -webkit-border-radius: 0px 0px 0px 4px; border-radius: 0px 0px 0px 4px; behavior: url(PIE.htc);}
.nt-corner-top { -moz-border-radius: 4px 4px 0px 0px; -webkit-border-radius: 4px 4px 0px 0px; border-radius: 4px 4px 0px 0px; behavior: url(PIE.htc);}
.nt-corner-bottom { -moz-border-radius: 0px 0px 4px 4px; -webkit-border-radius: 0px 0px 4px 4px; border-radius: 0px 0px 4px 4px; behavior: url(PIE.htc);}
.nt-corner-right { -moz-border-radius: 0px 4px 4px 0px; -webkit-border-radius: 0px 4px 4px 0px; border-radius: 0px 4px 4px 0px; behavior: url(PIE.htc);}
.nt-corner-left { -moz-border-radius: 4px 0px 0px 4px; -webkit-border-radius: 4px 0px 0px 4px; border-radius: 4px 0px 0px 4px; behavior: url(PIE.htc);}
.nt-corner-all { -moz-border-radius: 4px 4px 4px 4px; -webkit-border-radius: 4px 4px 4px 4px; border-radius: 4px 4px 4px 4px; behavior: url(PIE.htc);}