Remove background from header brand and top nav.

Use transparent text links; active state is accent color only.

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/更新说明.md

@@ -5,6 +5,14 @@
 
 ---
 
+## 2026-07-29 — 顶栏名称/导航去背景
+
+### 变更
+
+1. 标题区与顶部导航去掉底色/描边块，改为透明文字导航；选中项仅用强调色。
+
+---
+
 ## 2026-07-29 — 期权标题去掉指数（指数只在永续行情）
 
 ### 变更

frontend/src/styles/app.css

@@ -101,12 +101,7 @@ input {
   position: sticky;
   top: 0;
   z-index: 10;
-  background: linear-gradient(
-    180deg,
-    rgba(11, 14, 17, 0.98) 70%,
-    rgba(11, 14, 17, 0.88)
-  );
-  backdrop-filter: blur(8px);
+  background: transparent;
 }
 
 .brand-row {
@@ -126,6 +121,7 @@ input {
   white-space: nowrap;
   min-width: 0;
   font-size: clamp(16px, 1.35vw, 20px);
+  background: transparent;
 }
 
 .brand-actions {
@@ -146,13 +142,14 @@ input {
   flex-wrap: wrap;
   align-items: center;
   gap: 8px;
+  background: transparent;
 }
 
 .top-nav a {
-  padding: 8px 14px;
-  border: 1px solid var(--line);
-  border-radius: 8px;
-  background: var(--bg-elev);
+  padding: 8px 12px;
+  border: none;
+  border-radius: 0;
+  background: transparent;
   color: var(--muted);
   text-decoration: none;
   font-size: 15px;
@@ -162,12 +159,12 @@ input {
 
 .top-nav a:hover {
   color: var(--text);
-  border-color: rgba(240, 185, 11, 0.35);
+  background: transparent;
 }
 
 .top-nav a.active {
-  background: rgba(240, 185, 11, 0.12);
-  border-color: rgba(240, 185, 11, 0.45);
+  background: transparent;
+  border: none;
   color: var(--accent);
 }