Set email content headers to 100%

Currently the actual email header we have set to 100%. Looks good on mobile and on computer as it sized to fit regardless.

We aren't providers access to the headers for email content such as Booking Confirmations aren't which appears to be set to x number of pixels wide.

It would look much better if this were set to 100% as it would resize with the window/screen size like our email header email content.

See below for which header I am referring to: