For your convenience, we also provide a stylesheet for you to include if you want your integration to match our styles. Not only does it accelerate development, it will also make your integration support all of our themes by default. Check out our CSS styleguide.
<link href="https://integrations.missiveapp.com/missive.css" rel="stylesheet">
https is required when adding a custom integration to Missive. During development, we suggest using a tool like Caddy or Ngrok to create a secure tunnel to your local development server.