refactor: 更新固定标签页表头样式

Author: ArgoZhang

src/BootstrapBlazor/Components/Layout/Layout.razor.scss

@@ -233,22 +233,10 @@
     }
 
     &.is-fixed-tab {
-        .layout-main {
-            height: calc(var(--bb-layout-height) - var(--bb-layout-header-height) - var(--bb-layout-footer-height));
-        }
-
-        .tabs-body {
-            height: calc(100% - var(--bb-tabs-item-height));
-            overflow: auto;
-
-            .tabs-body-content {
-                height: auto;
-                min-height: 100%;
-            }
-        }
-
-        &:not(.has-footer) {
-            --bb-layout-footer-height: 0;
+        .tabs-header {
+            position: sticky;
+            top: var(--bb-layout-header-height);
+            z-index: 5;
         }
     }
 }