dots/usr/share/themes/Dracula/gtk-3.0/widgets/notebook.css

/************
 * notebook *
 ************/
.notebook {
    padding: 0;
    background-color: @theme_base_color;
    background-image: none;
    background-clip: border-box;
    -GtkNotebook-has-tab-gap: false;
    border: none;
}

.notebook.header {
    background-color: @theme_bg_color;
    background-image: none;
    box-shadow: none;
    border-width: 0;
}

.notebook tab {
    padding: 8px;
    box-shadow: none;
    border: 1px solid @theme_bg_color;
    background-color: alpha(@theme_base_color,0.3);
    background-image: none;

}

.notebook tab:active {
    background-color: @theme_base_color;
    /*border-left: 3px solid @selected_bg_color;*/
}

.notebook tab.top:active {
    border-bottom: 0px;
}

.notebook tab.left {
    border-right: 1px solid @theme_bg_color;
}

.notebook tab.left:active {
    border-right: 0px;
}

.notebook tab.bottom {
    border-top: 1px solid @theme_bg_color;
}

.notebook tab.bottom:active {
    border-top: 0px;
}

.notebook tab.right {
    border-left: 1px solid @theme_bg_color;
}

.notebook tab.right:active {
    border-left: 0px;
}

.notebook tab.left:first-child:active,
.notebook tab.right:first-child:active {
    border-top: 0px;
}

.notebook tab.left:last-child:active,
.notebook tab.right:last-child:active {
    border-bottom: 0px;
}

.notebook tab.top:first-child:active,
.notebook tab.bottom:first-child:active {
    border-left: 0px;
}

.notebook tab.top:last-child:active,
.notebook tab.bottom:last-child:active {
    border-right: 0px;
}

/* close button styling */
.notebook tab .button {
    transition: ease-in 150ms;
    padding: 2px;
    border: none;
    background-image: none;
    background-color: transparent;
    color: @theme_text_color;
}

.notebook tab .button:hover,
.notebook tab .button:active:hover {
    color: @red;
    background-color: transparent;
}