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

/******************
 * combobox entry *
 ******************/
GtkComboBox*:hover {
color: @selected_fg_color;
}

GtkComboBox .button {
    padding: 5px 6px 5px 6px;
}

GtkComboBox.combobox-entry .button {
    border-color: alpha(black,0.2);
}

GtkComboBox.combobox-entry .button:hover {
    border-color: transparent;
    border-top-color: alpha(white,0.2);
    border-bottom-color: alpha(black,0.2);
}

.primary-toolbar GtkComboBox.combobox-entry .entry,
.primary-toolbar GtkComboBox.combobox-entry .entry:active,
.primary-toolbar GtkComboBox.combobox-entry .entry:focus,
.primary-toolbar GtkComboBox.combobox-entry .entry:insensitive,
GtkComboBox.combobox-entry .entry,
GtkComboBox.combobox-entry .entry:active,
GtkComboBox.combobox-entry .entry:focus,
GtkComboBox.combobox-entry .entry:insensitive {
    border-top-right-radius: 0;
    border-bottom-right-radius: 0;
}

.primary-toolbar GtkComboBox.combobox-entry .button,
.primary-toolbar GtkComboBox.combobox-entry .button:hover,
.primary-toolbar GtkComboBox.combobox-entry .button:active,
.primary-toolbar GtkComboBox.combobox-entry .button:insensitive,
GtkComboBox.combobox-entry .button,
GtkComboBox.combobox-entry .button:hover,
GtkComboBox.combobox-entry .button:active,
GtkComboBox.combobox-entry .button:insensitive {
    border-bottom-left-radius: 0;
    border-top-left-radius: 0;
    border-left-width: 0px;
}
.linked-entry .entry {
    border-color: alpha(white,0.2);
}