gtk-3.css

/* better readability */

menu separator {
    margin-top: 4px;
    margin-bottom: 4px;
}
popover.background separator.horizontal {
    margin-top: 6px;
    margin-bottom: 6px;
}

.dim-label, .titlebar.subtitle {
    opacity: 0.8;
}

progressbar.horizontal trough,
progressbar.horizontal progress {
    min-height: 8px;
}
progressbar.vertical trough,
progressbar.vertical progress {
    min-width: 8px;
}
levelbar trough {
    min-height: 7px;
}


/* custom changes */

filechooser #pathbarbox {
    background: none;
    border-bottom: 1px solid @unfocused_borders;
}

.nautilus-window treeview, filechooser treeview {
    padding: 2px;
    -GtkTreeView-horizontal-separator: 5;
}

toolbutton button {
    -gtk-icon-style: symbolic;
}



/* dialogs */

* {
    -GtkDialog-action-area-border: 5;
}

messagedialog {
    -GtkDialog-action-area-border: 0;
    -GtkWidget-window-dragging: true;
}

messagedialog .dialog-action-area button {
    padding-top: 8px;
    padding-bottom: 8px;
}
messagedialog .titlebar .title {
    margin-top: 1px;
    opacity: 0.7;
}
messagedialog .titlebar {
    min-height: 0;
}
messagedialog .dialog-vbox {
    margin-top: 11px;
}


/* sync with GTK4 */

.titlebar > .right, .titlebar > headerbar > .right {
    margin-left: -6px;
}

popover.menu {
    background: @content_view_bg;
}
popover.menu modelbutton.flat:hover {
    background-color: shade(@content_view_bg, 0.85);
}