Hi,

1) The easiest (but not the only) way is Page->Responsive->100% width. Unless you've used one of ancient templates where soem styles may block this operation.

2) OE is a WYSIWYG "generator" and the resulting HTML code is not supposed to be edited. You can manipulate properties and styles of elements, or modify/create custom elements (Elements->Create). You can, however, add HTML, CSS, JS or PHP code into Code Blocks, which are of 2 types - Visual (somewhere in the middle of the page body, wherever you place them) and Source (in specific places like head section)