My TST config

personal_tst.css

/* Adjust style for tab that has sound playing. */
.tab.sound-playing .label:before {
  content: " 🔊  ";
}

/* Show title of unread tabs with red and italic font */
/*
.tab.unread .label {
  color: red !important;
  font-style: italic !important;
}
*/

/* Add private browsing indicator per tab */
/*
.tab.private-browsing .label:before {
  content: "🕶";
}
*/

/* Change styling of pending (unloaded) tabs */
.tab.discarded {
  opacity: 0.85;
}

/* Less visible tab dividers. 
   A black border with a very low alpha slightly darkens any color. */
.tab {
  border: solid 1px #00000012; 
}

/* I don't need a damn close button */
.tab .closebox {
  display: none;
}

/* Hide the "new tab" button at the bottom edge of the tab bar */
.newtab-button-box {
  display: none;
}

#tabbar {
  bottom: 0 !important; /* Eliminate dead space on bottom */
}

/* Container tabs background color */
.contextual-identity-marker {
  position: absolute !important;
  pointer-events: none;
  z-index: 0;
  
  bottom: 0 !important;
  left: 0 !important;
  right: 0 !important;
  top: 0 !important;
  
  width: unset !important;
  height: unset !important;  
    
  opacity: 0.5;
}