How to configure gvim8 tab’s gtk3 css style?

  question, vim

Gvim 8 is based on gtk3. how do you define tab style in ~/.config/gtk-3.0/gtk.css?

To view the element structure with gtkspector:

GTK_DEBUG=interactive gvim
@define-color VIM_BG_FIX #3C4C55;
 
 window#vim-main-window {
 background-color: @VIM_BG_FIX;
 }
 
 window#vim-main-window notebook header {
 background-color: #1E272C;
 border-bottom-width: 0;
 }
 window#vim-main-window notebook tab {
 border-bottom-width: 0;
 }
 window#vim-main-window notebook tab label {
 padding-left:5px;
 padding-right:5px;
 padding-top:1px;
 padding-bottom:2px;
 color: #7CBDC6;
 }
 window#vim-main-window notebook tab:checked label {
 background-color: #7CBDC6;
 color: #1E272C;
 }