One last thing to know about CSS — it's also valid to code in-line CSS, where the style is specified
inside the HTML tag as an attribute.
<button style="background-color:gold"> Click me </button>
This is
considered bad form, for the same reason applying style to #IDs is considered bad form — you're
missing out on most of the power of CSS and making life harder for yourself later.
You may notice we used in-line CSS in the S2JS canvas element. Naughty us! We took that approach in the interests of simplicity.
As you progress, you'll see times it makes sense to break this guideline.
But to begin with, just avoid in-line CSS.