As promised! (https://app.box.com/s/pjhnglffjlbjvtjh425wy1gzosxzsyyf).
(duplicate your Magnesium theme, i.e. Magnesium Copy)
Replace in Magnesium Copy folder:
index.html
styles.css
In RapidWeaver:
Code CSS: copy/paste contents of code.css
Code Head: <meta name="viewport" content="width=device-width, initial-scale=1, viewport-fit=cover" />