Add scroll to top button

src/components/layouts/Honkai3rdLayout.tsx

@@ -1,18 +1,42 @@
 /** @jsxImportSource theme-ui */
 
-import { mdiMenu } from '@mdi/js'
+import { mdiArrowUp, mdiMenu } from '@mdi/js'
 import Icon from '@mdi/react'
-import React, { useCallback, useState } from 'react'
+import React, { useCallback, useRef, useState } from 'react'
 import { Box, Flex, IconButton } from 'theme-ui'
 import Honkai3rdNavigator from '../organisms/Honkai3rdNavigator'
 
 const Honkai3rdLayout: React.FC = ({ children }) => {
   const [hiddenMobileNav, setHiddenMobileNav] = useState(true)
+  const contentBoxRef = useRef<HTMLDivElement>(null)
+  const [scrolled, setScrolled] = useState(false)
 
   const close = useCallback(() => {
     setHiddenMobileNav(true)
   }, [])
 
+  const handleScroll = useCallback(() => {
+    if (contentBoxRef.current == null) {
+      return
+    }
+
+    if (contentBoxRef.current.scrollTop === 0) {
+      return setScrolled(false)
+    }
+    if (scrolled) {
+      return
+    }
+    setScrolled(true)
+  }, [scrolled])
+
+  const scrollToTop = useCallback(() => {
+    if (contentBoxRef.current == null) {
+      return
+    }
+
+    contentBoxRef.current.scrollTop = 0
+  }, [])
+
   return (
     <Flex
       sx={{
@@ -33,14 +57,40 @@ const Honkai3rdLayout: React.FC = ({ children }) => {
       >
         <Honkai3rdNavigator close={close} />
       </Box>
-      <Box sx={{ flex: 1, overflowY: 'auto', overflowX: 'hidden' }}>
+      <Box
+        sx={{
+          flex: 1,
+          overflowY: 'auto',
+          overflowX: 'hidden',
+          scrollBehavior: 'smooth',
+        }}
+        onScroll={handleScroll}
+        ref={contentBoxRef}
+      >
+        <IconButton
+          sx={{
+            width: 50,
+            height: 50,
+            position: 'absolute',
+            bottom: 1,
+            right: 1,
+            zIndex: 1000,
+            pointerEvents: scrolled ? 'auto' : 'none',
+            opacity: scrolled ? 1 : 0,
+            transition: 'opacity 200ms ease-in-out',
+            backgroundColor: 'transparent',
+          }}
+          onClick={scrollToTop}
+        >
+          <Icon path={mdiArrowUp} size={1} />
+        </IconButton>
         <Flex
           sx={{
             position: 'sticky',
             display: ['block', 'none'],
             top: 0,
             height: 50,
-            bg: 'rgba(255,255,255,0.8)',
+            bg: 'transparent',
           }}
         >
           <IconButton