CSS in relation to pages could be edited in 3 different locations.
Block level - This is what you have already seen, whereby the block itself has CSS sections you can enter
Pages templates - Pages has its own set of templates, of which control how pages and databases display. You can see these in Pages->Page Management->Templates . There is a CSS. This is where you would create full custom wrappers if you wish to do so
Theme level - For most people, this would be where you would change CSS. You find this in Customization->Appearance->Themes, by selecting the </> icon at the side of your theme. Here you can edit the way your site looks as a whole, in every way. If you want to add or override CSS elements, generally you would add to the custom.css file you can see on the CSS tab. This is never changed on upgrades, and is loaded last in the cascade (therefore you can use this to override any CSS element)
While we cannot assist with customization itself, you can take a look through our guides in the following location, which has more information on the above areas and much more