fix: 面板「+」按钮样式与浏览器页签栏「+」保持一致（幽灵样式）

apps/desktop/src/renderer/src/components/SidePanel.tsx

@@ -206,13 +206,11 @@ export function SidePanel({
                 aria-label="打开新的标签"
                 title="打开新的标签"
                 onClick={() => setPlusOpen((v) => !v)}
-                className={`flex size-7 items-center justify-center rounded-md border transition-colors ${
+                className={`flex size-7 shrink-0 items-center justify-center rounded transition-colors ${
-                  plusOpen
+                  plusOpen ? 'bg-zinc-100 text-zinc-600' : 'text-zinc-400 hover:bg-zinc-100 hover:text-zinc-600'
-                    ? 'border-accent/50 bg-accent-tint/40 text-accent-ink'
-                    : 'border-zinc-200 bg-white text-zinc-400 hover:border-accent/40 hover:text-zinc-600'
                 }`}
               >
-                <LuPlus size={12} />
+                <LuPlus size={13} />
               </button>
 
               {plusOpen && (