style(admin): 侧边栏父菜单(分组)标题字号加大至 15px 并加深色

admin-frontend-vue/src/styles/main.css

@@ -82,7 +82,7 @@ button, input, textarea, select { font: inherit; }
 }
 .admin-menu .el-menu { background: transparent; }
 .admin-menu .el-sub-menu .el-sub-menu__icon-arrow { color: var(--admin-sidebar-text); }
-.menu-group-title { font-size: 12px; font-weight: 600; letter-spacing: 1.1px; color: #72859a; }
+.menu-group-title { font-size: 15px; font-weight: 600; letter-spacing: .4px; color: var(--admin-sidebar-text); }
 .menu-group-title:hover { color: var(--admin-primary-strong); }
 
 .sidebar-collapse {