Is all the CSS written inside the HTML file, or would it be written in a separate file

Is there something comparable to the box model for inline elements? 

id tags vs other types of tags - how to use them to select items

Could you share examples of how more than one style can be applied to something and how it would appear on a browser as a result?

When to use what unit for images and whatnot. Is there an option that is always better and should be used a majority of the time?

More clarification on class vs id please

In what situation do we use tag selector?

Selectors and Ids , is there a quick way to understand them

"What does this mean?

This rule happens to apply to the hyperlinks that surround each picture. (You can look back at the HTML to see all the elements that are class=""thumbnail-item-a"".) 

I am confused about the content after the ="



"A bit confused on the purpose of normalize.css, what does it mean when it says ""to have a consistent basis for styling pages""? Why would we need this? I thought stuff like class would take care of styling consistency, unless I'm misinterpreting this?

Also confused about how inline-block works, how display: inline-block works, and how display:  list-item works"
/ Difference between & more practices on block, inline-block, and inline

can we talk more about why some people don't like ids and what the benefits of using them are?

Could we have more practice with the CSS rules and just overall review over the syntax?

Difference between em and rem