NautilusWindow {
   background-image: url ("../assets/background0.png");
   background-repeat: no-repeat;
   background-position:bottom right;
   background-size: 50px;
}
NautilusWindow .sidebar .frame {
   background-image: linear-gradient(to bottom, @bg_color, alpha(@bg_color,0.5)), url("../assets/44148061_p0.jpg");
   background-size: 100%;
   background-repeat: no-repeat;
   background-position:bottom right;
}
NautilusWindow .sidebar GtkTreeView {
   background-color: @transparent;
}
NautilusCanvasViewContainer,
NautilusListView GtkTreeView,
NautilusListView GtkTreeView GtkButton {
   background-color: @transparent;
}
.nautilus-canvas-item {
   border-radius: 4px;
   background-color: @selected_bg_color;
}
/* 以上部分是经过我的修改的 */


NautilusWindow * {
    -GtkPaned-handle-size: 1;
}
NautilusDesktopWindow GtkWidget {
    background-color: @transparent;
}


/* desktop mode */
.nautilus-desktop.nautilus-canvas-item {
    color: @bg_color;
    text-shadow: 1px 1px alpha (#000000, 0.8);
}

.nautilus-desktop.nautilus-canvas-item:active {
    background-image: none;
    background-color: alpha (@bg_color, 0.84);

    color: @fg_color;
}

.nautilus-desktop.nautilus-canvas-item:selected {
    background-image: none;
    background-color: alpha (@selected_bg_color, 0.84);

    color: @selected_fg_color;
}

.nautilus-desktop.nautilus-canvas-item:active,
.nautilus-desktop.nautilus-canvas-item:prelight,
.nautilus-desktop.nautilus-canvas-item:selected {
    text-shadow: none;
}
[/css]

也不知道 nautilus.css 文件改错了没有，为什么连个错误提示都没有呢？

我用 GtkInspector 修改的代码如下：
[code]
/*
You can type here any CSS rule recognized by GTK+.
You can temporarily disable this custom CSS by clicking on the “Pause” button above.

Changes are applied instantly and globally, for the whole application.
*/

NautilusWindow {
   background-image: url("/home/liu/.themes/KanColle/gtk-3.0/assets/background0.png");
   //background-image: linear-gradient(to left, #aa0000, #00aa00);
   background-repeat: no-repeat;
   background-position:bottom right;
   background-size: 50%;
}
NautilusWindow .sidebar .frame {
   background-image: linear-gradient(to bottom, @bg_color, alpha(@bg_color,0.5)), url("/home/liu/.themes/KanColle/gtk-3.0/assets/44148061_p0.jpg");
   background-size: 100%;
   background-repeat: no-repeat;
   background-position:bottom right;

}
NautilusWindow .sidebar GtkTreeView {
   background-color: @transparent;
}
NautilusCanvasViewContainer,
NautilusListView GtkTreeView,
NautilusListView GtkTreeView GtkButton {
   background-color: @transparent;
}
.nautilus-canvas-item {
   background-color: @selected_bg_color;
}