A css rule is containing a selector and declaration block.
It Selects all the elements that comply with given node name or based on the element name.
Example: input will check any <input> element.
It Selects all elements with a specific class attribute or which have the given class attribute.
Example: .index will match any element that has a class of "index".
The ID selector Selects an element based on the value of its id attribute. There should be only unique element with a given ID.
Example: #age will check the element that has the given ID "age".
The Universal selector Selects all the elements. but, Rather than selecting elements the universal selcector selects that match quitely with any type of element that match.
Syntax: * Note|* *|*
Example: * (asterisk) will check all the elements in our document.
The Attribute selector selects all elements based on the value of the given type of attribute.
Syntax: [attr] [attr$=value] [attr#=value]
Example: [autoplay] will check all elements in which the autoplay attribute is set (with thier value).
A property is a type of attribute of HTML tag or element it defines what charateristic to alter it could be alter by any HTML element like color, border etc.
Values are allowed to CSS properties and the interactions between them.