The tab widget is a handy tool to display more information on one page in a structured way. Formatting can be a bit tricky, here are some hints:
Default tab box comes with little tab-handles and a white border around the area.

Format the handle
Classs/Pseudoclass QTabBar::tab
Supported formating options
background-color | |
padding | |
margin | |
color | |
border | border-left, border-right, border-top, border-bottom |
Format the selected handle
QTabBar::tab:selected {
margin-bottom: -1px;
}
Format the tab area
QTabWidget::pane {
top:-1px;
background-color:#ffcc66;
}
Some examples
[group="tab_noborder"][darkTheme="true"]{
border:0px;
}