Answer 1

You can not remove that.That is hard coded into the platform. That is where your first blog post will be displayed.

Answer 2

You can change the background color of it or make it transparent in th advanced options.

Answer 3

maybe something like using

" 'white-box-selector' {
display: none;
}"

but if you want it displayed when you have posts, probably best to use JS to hide/show the white box conditionally