style: update TOC button styling in README view

- Remove border from the TOC button in the README view for a cleaner appearance.
- Ensure hover state maintains no border for consistency with the overall design.

templates/repo/view_file.tmpl

@@ -36,7 +36,7 @@
 		</div>
 		<div class="file-header-right file-actions flex-text-block tw-flex-wrap">
 		{{if .FileSidebarHTML}}
-			<button class="btn-octicon" id="toggle-sidebar-btn" data-tooltip-content="{{ctx.Locale.Tr "toc"}}">{{svg "octicon-list-unordered" 15}}</button>
+			<button class="btn-octicon" id="toggle-sidebar-btn" data-tooltip-content="{{ctx.Locale.Tr "toc"}}">{{svg "octicon-list-unordered"}}</button>
 		{{end}}
 			{{/* this componment is also controlled by frontend plugin renders */}}
 			<div class="ui compact icon buttons file-view-toggle-buttons {{Iif .HasSourceRenderedToggle "" "tw-hidden"}}">

web_src/css/repo/home.css

@@ -187,6 +187,15 @@
   border-color: var(--color-primary);
 }
 
+/* README view: TOC button should not have border */
+#readme .file-header-right #toggle-sidebar-btn {
+  border: none;
+}
+
+#readme .file-header-right #toggle-sidebar-btn:hover {
+  border: none;
+}
+
 /* Sidebar toggle button active state - when sidebar is visible */
 #toggle-sidebar-btn.active {
   color: var(--color-primary);