CSS Selectors

#css

Universal selector

* - targets all elements on the page

Element/tags

Target all p elements

p { 
  color: red; 
}

IDs

IDs must be unique on a page and are targeted using a # (hash) e.g.

#my-page { 
  background-color: yellow; 
  color: red;
}

Classes

Classes are reusable and can be added to multiple elements to target them use . (dot) notation e.g.

.some-nav { 
  display: flex; 
}

Sibling and adjacent selectors

Descendant combinator This is represented by a space between selectors e.g.

main p { 
  padding: 1rem 0; 
}

Child combinator > - this is placed between two selectors and will match only elements that are direct children of the first element e.g.

div > span { 
  background-color: #333; color: #fff; 
}

General Sibling combinator ~ - this will match all iterations of the second element following the first and are children of the same parent

// Targets any paragraphs that are siblings of and follow h2 
h2 ~ p { 
  color: blue; 
}

Adjacent sibling combinator + - this will match the second element only if it directly follows the first element and both have the same parent e.g.

// Any paragraphs that follows a h2 element 
h2 + p { 
  color: red; 
}

Pseudo Classes

I have used several of these, but there are a couple I use for every project these are:

:root - this targets the root element usually this is html
:hover - can use this to change styling of an element when hovering over it with a pointing device e.g.

a { color: #CC0000; } 
a:hover { color: #000000; font-weight: bold; }

Pseudo Elements

These are added to a selector to target styling on a specific part of the selected element(s).

There are few that are available some of which I've never used but probably the most common are:

::first-line - style the first line of a paragraph
::first-letter - targets the first letter e.g.in a newspaper style
::before - the first child of the selected element often used with content for UI improvements one example may be to add quote marks or change the look of list elements
::after - as above but the last child of the selected element

*Note the double colon is used to distinguish between pseudo elements and pseudo classes e.g.

.intro::first-letter { 
  font-size: 3rem; 
  padding-right: 1rem; 
} 

.intro::first-line { 
  font-weight: bold; 
} 

a::before { 
  content: '◆'; 
}

Attribute Selectors

These are surrounded by []

[attr=value] - exact match value
[attr^=value] - starts with
[attr*=value] - contains
[attr$=value] - ends with
[attr~=value] - elements with an attribute name of attr whose value is a whitespace-separated list of words one of which is exactly value and a new one I learnt researching these:
[attr operator value i] - adding i causes a case insensitive comparison for those in ASCII range having never used does anyone have a use case for this?

a[title]{ 
  color: green; 
} 

a[href^="https://"]{ 
  color: red; 
}

a[href$=".com"]{ 
  color: blue; 
}

There are a few examples of some common and some useful selectors let me know if you think there are others I should have mentioned I'm sure there are!