QTabBar::tab with border causes tab text to disappear

In the following stylesheet for QTabBar::tab, adding a border (e.g. border-top) causes the tab text to disappear:

QTabBar::tab

{     background: #DFE7EF;     color: #393F41;     font-family: "Noto Sans ExtraLight";     font-size: 26px;     border-top: 1px solid #fff; }

If the border line is removed, the text appears correctly again.