fix: 修复按钮样式和分类弹窗样式

- 侧边栏按钮添加间距
- 添加分类按钮使用次要样式
- 添加网站按钮使用主样式
- 添加缺失的分类管理弹窗CSS样式

frontend/src/App.jsx

@@ -211,7 +211,7 @@ function App() {
         </div>
 
         <div className="sidebar-footer">
-          <button className="add-btn" onClick={openCategoryModal}>
+          <button className="add-btn secondary" onClick={openCategoryModal}>
             <Icon name="folder" size={14}/><span>添加分类</span>
           </button>
           <button className="add-btn" onClick={() => openWebsiteModal()}>

frontend/src/index.css

@@ -173,6 +173,9 @@ body {
 .sidebar-footer {
   padding: 16px;
   border-top: 1px solid rgba(0, 0, 0, 0.05);
+  display: flex;
+  flex-direction: column;
+  gap: 8px;
 }
 
 .add-btn {
@@ -198,6 +201,18 @@ body {
   box-shadow: 0 6px 16px rgba(102, 126, 234, 0.4);
 }
 
+.add-btn.secondary {
+  background: rgba(255, 255, 255, 0.95);
+  color: #667eea;
+  border: 1.5px solid #667eea;
+  box-shadow: none;
+}
+
+.add-btn.secondary:hover {
+  background: #667eea;
+  color: white;
+}
+
 /* ===== 主内容区 ===== */
 .main-content {
   flex: 1;
@@ -691,6 +706,122 @@ body {
   box-shadow: 0 6px 16px rgba(102, 126, 234, 0.4);
 }
 
+.btn-submit:disabled {
+  opacity: 0.5;
+  cursor: not-allowed;
+  transform: none;
+}
+
+/* ===== 分类管理弹窗 ===== */
+.category-form {
+  padding-bottom: 16px;
+  border-bottom: 1px solid #f0f0f0;
+  margin-bottom: 16px;
+}
+
+.form-row {
+  display: flex;
+  gap: 8px;
+  margin-bottom: 12px;
+}
+
+.form-row .form-input {
+  flex: 1;
+}
+
+.color-picker-row {
+  display: flex;
+  gap: 8px;
+  flex-wrap: wrap;
+}
+
+.color-option {
+  width: 32px;
+  height: 32px;
+  border-radius: 8px;
+  border: 2px solid transparent;
+  cursor: pointer;
+  transition: all 0.2s ease;
+}
+
+.color-option:hover {
+  transform: scale(1.1);
+}
+
+.color-option.selected {
+  border-color: #333;
+  box-shadow: 0 0 0 2px white;
+}
+
+.category-list {
+  max-height: 300px;
+  overflow-y: auto;
+}
+
+.category-list-item {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  padding: 10px 12px;
+  border-radius: 8px;
+  transition: background 0.2s ease;
+}
+
+.category-list-item:hover {
+  background: #f5f5f5;
+}
+
+.category-list-info {
+  display: flex;
+  align-items: center;
+  gap: 8px;
+}
+
+.category-list-color {
+  width: 12px;
+  height: 12px;
+  border-radius: 50%;
+}
+
+.category-list-name {
+  font-size: 13px;
+  color: #333;
+}
+
+.category-list-count {
+  font-size: 11px;
+  color: #999;
+}
+
+.category-list-actions {
+  display: flex;
+  gap: 4px;
+}
+
+.category-list-actions button {
+  width: 28px;
+  height: 28px;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+  border: none;
+  background: transparent;
+  color: #999;
+  cursor: pointer;
+  border-radius: 4px;
+  transition: all 0.2s ease;
+}
+
+.category-list-actions button:hover {
+  background: #e0e0e0;
+  color: #333;
+}
+
+.category-list-actions button:last-child:hover {
+  background: #fee;
+  color: #f44;
+}
+
 /* ===== 加载 ===== */
 .loading {
   display: flex;