In this lesson you'll learn the syntax of CSS and
begin learning some CSS selectors.
Selectors are what you use to select and style one or
more elements on your HTML page: you can use very
basic selectors that style all occurrences of a specific
element, and more complex selectors that select specific
elements on the page. In this lesson you'll start with
basic element selector, id and class selectors, and
attribute selectors. In later lessons you'll learn more
CSS is made up of rules or rule-sets.
A rule defines how something should be formatted.
A rule consists of one or more selectors
and a declaration block.
For example, in the picture below, there is a single CSS rule.
The selector defines which elements are being
styled. In the example above, the rule is styling all of
the <aside> elements.
The declaration block
defines how those elements should be styled.
It contains one or more declarations,
each of which assigns a value
to a specific CSS property. For example,
in the picture above,
the declaration block contains 3 declarations. The first one
defines the thickness, style, and colour of the <aside>
border. The other two declarations defines the amount of
around the outside of <aside> elements and the amount
of padding space around
the inside of the <aside> elements' borders.
named in a declaration are part of the
In the example above, we are assigning values to 3 properties: the
border property, margin property, and padding property.
you're allowed to assign to each property are also part
For example, a font-colour property can
take any one of several pre-defined colour names.
There are several different kinds of selectors in CSS. You must
already be familiar with HTML and the basic elements in order to understand
CSS selectors. If you're not comfortable knowing your HTML elements,
you might wish to pause and review
A selector selects a set of
elements to apply a rule (collection of declarations or
styles) to. Basically, a selector
tells the browser to go through a document and find
all of the elements that match that selector. For example, a
section selector will tell
the browser to go and find all <section> elements in the document
and style them according to the declarations inside that rule's
There are different categories of selectors, depending
on how you want to select elements: do you want to select
all of a certain type of element, or only elements with a
certain attribute (or even a certain attribute value)?
What if you wanted to style only some <section> elements
but not others? What if you wanted to style one specific
<img> element on the page, even though there are several
<img> elements? What if you wanted to style just a single
word, or the first line of a paragraph? You can do all of
these things with selectors, although this lesson covers only
basic element selectors. We'll cover other kinds of
selectors later, and more advanced selectors in
An element selector (also called a type selector)
is used when you want to define styles
for specific elements in a document. The element selector
has the same name as the element. For example, to style all
<h1> elements, you use the h1
selector, and to style all <p> elements you use the
In the example above, we've defined a rule using the section
selector. This tells the browser to find all <section> elements
and give them a grey background, navy text, a margin
around the outside of the section (.2em means
it is set to be 20% of the
section's font size), and some padding space
around the inside border of the section
(.3em means 30% of the section's font size).
You'll learn more about
those properties and their values later.
Here's a CodePen example you can play with: this example
uses element selectors for the <h1>, <h2>, and
<strong> elements to change the colours of those
elements on the page.
There are other types of selectors: some of the upcoming
examples will use these selectors, but they'll be
covered in later lessons. However, if you would like to
learn about these selectors now, here are the available
As mentioned previously, a declaration assigns a value to
a specific property. A declaration is a single
statement inside a CSS rule that consists of a property,
followed by a colon, followed by the value you want to
assign to the property. For example:
This single declaration changes the value of the color
property to "red".
How do we know what the property names are? How do we know
what values each property is allowed to recieve? All of this
is defined in the CSS specification on W3C, such as in
the CSS Properties Index and
CSS Values Index. However, you can
also find lots of other CSS reference pages online, such as:
The CSS properties are divided up into Modules, so it might
be easier to learn CSS properties by module or category,
instead. This is how the remaining CSS tutorials in this
course will cover CSS properties.
The values each property receives depends on the property:
Each property has a specific type of values it's allowed to
accept. Some values are measurements, some properties take
one of a set of pre-defined values.
Values and Data Types summarizes
the values and units used by CSS.