CSS Syntax
CSS syntax contains set of rules. These rules have 2 parts: a selector, and declaration (property, and a value).
The selector indicates the HTML element you want to style, like any tag <h1>, <p> etc.
The declaration block consists of one or more declarations separated by semicolons.
Each declaration contains a CSS property name and a value, separated by a colon.
The declaration blocks are surrounded by curly braces and each CSS declaration ends with a semicolon.
CSS Comments
CSS comments are used to explain a block of code or to make temporary changes during development. Comments are ignored by browsers. A comment are single line or multiple lines starts with /* and ends with */.
CSS does not support inline comments, like // in C or JavaScript. If you insert // before a property, that property will not be applied, looking like the comment worked. But in reality, CSS detected a syntax error and due to how it works it ignored the line with the error, and went straight to the next line. Knowing this approach lets you purposefully write inline comments, although you have to be careful because you can’t add random text like you can in a block comment.
Case Sensitivity in CSS
The CSS property names and many values are not case-sensitive. But, CSS selectors are usually case-sensitive, for example, the class selector .firstHeading is not the same as .firstheading. Therefore, to be on safer side, you should assume that all components of CSS rules are case-sensitive.