Feat/account

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We're just taking the styles that are specific to a "floating" page (like the way that padding works on the hero, the way that sections are separated by headers with underlines etc) and the most important bit - the part where the sections do not get a white background by default, and turning it into a mixin. Here, I am following the pattern of a named non-matching selector (`$floating`) and a mixin (`floating()`) to make the syntax for including simple while maintaining the benefits of using `@extend