a) how to resize the optin form, b) how to change the background colour of the optin form, c) how to imply left and right arrows into my optin form.
Here’s how to change the background color of your opt-in:
You can’t really resize the form per se. It will reflow to fill whatever size your row is (so if it is a row that stretches across the page, it will fill this. If it is a multi-column row, then it would fill that and be slightly smaller.
You can adjust horizontal and vertical padding, see screenshot below.
There’s no way currently to add arrow graphics or icons to the form. Though you could create a “subscribe button” graphic that has arrows and then upload and use it, see screenshot below.