fix: wrong cascading relationship (#3800)

(cherry picked from commit 4d58f2b4c7)

apps/core/src/components/pure/header/style.css.tsx

@@ -8,6 +8,7 @@ export const header = style({
   padding: '0 16px',
   minHeight: '52px',
   borderBottom: '1px solid var(--affine-border-color)',
+  zIndex: 2,
   selectors: {
     '&[data-sidebar-floating="false"]': {
       WebkitAppRegion: 'drag',

apps/core/src/components/pure/trash-button-group/styles.css.ts

@@ -8,6 +8,7 @@ export const group = style({
   display: 'flex',
   gap: '24px',
   justifyContent: 'center',
+  zIndex: 2,
 });
 export const buttonContainer = style({
   boxShadow: 'var(--affine-float-button-shadow-2)',