Userscript
If you know some coding, you can customize Scrapbox by adding style.css and script.js Code blocks to your Profile page.
To use customization, enable user script by going to https://scrapbox.io/settings/extensions and then add any user script you want.
After adding or updating script, reload the page and you should see a message to Load new user script.
Note: Customization will only be visible to you.
Example:
Add a Google Translate Button (EN --> JA)
code:script.js
scrapbox.PopupMenu.addButton({
title: 'Translate',
onClick: text => window.open(https://translate.google.com/#en/ja/${text})
})