File browser CSS tweaks (#6738)

* File browser CSS tweaks

* Set tabsMovable to false

* Style file browser buttons

* Add missing headers

* Update Playwright Snapshots

* Update Playwright Snapshots

* Lint

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>

packages/application/style/base.css

@@ -59,7 +59,6 @@ body {
 }
 
 #main-panel {
-  box-shadow: var(--jp-elevation-z4);
   margin-left: auto;
   margin-right: auto;
   max-width: var(--jp-notebook-max-width);
@@ -71,6 +70,10 @@ body {
 
 /* Special case notebooks as document oriented pages */
 
+[data-notebook]:not(body[data-notebook='notebooks']) #main-panel {
+  box-shadow: var(--jp-elevation-z4);
+}
+
 body[data-notebook='notebooks'] #main-panel {
   margin-left: unset;
   margin-right: unset;

packages/tree-extension/src/index.ts

@@ -159,6 +159,7 @@ const notebookTreeWidget: JupyterFrontEndPlugin<INotebookTree> = {
 
     nbTreeWidget.addWidget(browser);
     nbTreeWidget.tabBar.addTab(browser.title);
+    nbTreeWidget.tabsMovable = false;
 
     // Toolbar
     toolbarRegistry.addFactory(

packages/tree-extension/style/base.css

@@ -0,0 +1,17 @@
+/*-----------------------------------------------------------------------------
+| Copyright (c) Jupyter Development Team.
+|
+| Distributed under the terms of the Modified BSD License.
+|----------------------------------------------------------------------------*/
+
+.jp-FileBrowser-toolbar .jp-Toolbar-item.jp-DropdownMenu,
+.jp-FileBrowser-toolbar .jp-Toolbar-item.jp-ToolbarButton,
+.jp-FileBrowser-toolbar .jp-Toolbar-item.jp-CommandToolbarButton {
+  border: solid 1px var(--jp-border-color2);
+  margin: 1px;
+  padding: 0px;
+}
+
+.jp-FileBrowser-toolbar button.jp-ToolbarButtonComponent {
+  height: 100%;
+}

packages/tree-extension/style/index.css

@@ -1,3 +1,11 @@
+/*-----------------------------------------------------------------------------
+| Copyright (c) Jupyter Development Team.
+|
+| Distributed under the terms of the Modified BSD License.
+|----------------------------------------------------------------------------*/
+
 @import url('~@jupyterlab/filebrowser/style/index.css');
 
 @import url('~@jupyter-notebook/tree/style/index.css');
+
+@import './base.css';

packages/tree-extension/style/index.js

@@ -1,3 +1,5 @@
 import '@jupyterlab/filebrowser/style/index.js';
 
 import '@jupyter-notebook/tree/style/index.js';
+
+import './base.css';

packages/tree/style/base.css

@@ -18,6 +18,7 @@
 }
 
 .jp-TreePanel .lm-TabBar-tab {
+  flex: 0 1 auto;
   color: var(--jp-ui-font-color0);
   font-size: var(--jp-ui-font-size1);
   height: 100%;