Move "core" folder out of "features" into "base"

src/base/components/virtuoso/StyledGroupHeader.tsx

@@ -0,0 +1,28 @@
+/*
+ * Copyright (C) Contributors to the Suwayomi project
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/.
+ */
+
+import { styled } from '@mui/material/styles';
+import { TypographyProps } from '@mui/material/Typography';
+import Stack from '@mui/material/Stack';
+import { shouldForwardProp } from '@/base/utils/ShouldForwardProp.ts';
+
+type StyledGroupHeaderProps = {
+    isFirstItem: boolean;
+};
+export const StyledGroupHeader = styled(Stack, {
+    shouldForwardProp: shouldForwardProp<StyledGroupHeaderProps>(['isFirstItem']),
+})<StyledGroupHeaderProps & TypographyProps>(({ theme, isFirstItem }) => ({
+    paddingLeft: theme.spacing(3),
+    paddingTop: theme.spacing(0.75),
+    paddingBottom: theme.spacing(2),
+    fontWeight: 'bold',
+    backgroundColor: theme.palette.background.default,
+    [theme.breakpoints.down('sm')]: {
+        paddingTop: isFirstItem ? theme.spacing(1) : theme.spacing(0.75),
+    },
+}));