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The module presents the concepts used in the CSS programming language.


Cascading Style Sheets (abbreviated CSS) are used to describe how (X)HTML or XML text is to be presented. This module is currently a commented link list of important entry points for reading about CSS.

This module gives a simple example how a CSS style sheet works.

Content of this module

Css rules

A CSS file consists of statements which are either at-rules or rule sets (often just called rules). A rule set (rule) consists of a selector and a declaration block which contains one or more declarations (more see CSS 2.1 specification ). A declaration contains a property and a value (e.g. "color" and "green"), see example below. These rules describe how the formatting should take place.

Below are some sample rules. In the first part one or several selectors are given and in the second part there are one or more attribute-value pairs enclosed by curly brackets.

/* Sample rules */ h1, h2 {color: green}#box {width: 70%} .topic {color: red}

    Selector types

  • h1 and h2 are tag selectors
  • #box is a selector for an identification
  • .topic is a selector for a class

A series of tests for selectors.

Internal and external style sheets

A style sheet may reside in a separate file ( external style sheet ) or within an (X)HTML file ( internal style sheet ).

External style sheet

<head><link rel="stylesheet" type="text/css" media="screen, projection, handheld, print" href="css/general.css" /><link rel="stylesheet" type="text/css" media="print" href="css/ourPrintStyleSheet.css" /></head>

In the case of the code above taken from a HTML file we load a general style sheet for different kinds of output media called general.css and a specific one for printing ( ourPrintStyleSheet.css ). The style sheet for printing adds and overrides some rules to put the content onto paper.

Internal stylesheet (html)

<style type="text/css">h1 { color: green;}</style>

Internal stylesheet (xhtml)

<style type="text/css"><![CDATA[ h1 {color: green; }]]></style>

@import rule

The @import rule ( ref. ) allows you to import rules from another style sheet into your current one. For an example see ´web fonts´ below.


CSS 2.1 specification (implemented by most browsers); an index

All W3C CSS standards and drafts

The link above includes the documents commonly called CSS 3 which consists of different modules. They are implemented to various degrees in the current browsers.


w3.org: Starting with HTML and CSS (basic introduction)

Complete course with interactive exercises w3schools

Searching for the key words css cheat sheet provides helpful links if you have learned CSS in the past. This brings up for example this list which leads to 30 examples .

Layout with css

For doing layout with CSS the 'position' attribute and the box model are used. In the past this was difficult because the box model implemented by the Internet Explorer (IE) differed from the web standard and from the box model implemented by other browsers. In the meantime the Internet Explorer supports the standard W3C box model so using CSS in modern browsers is made easier as there needs not to be a 'switch' anymore for IE and the other browsers. CSS 3 introduces the box-sizing property which allows to set how the box size is calculated ( (External Link) ).

Questions & Answers

what is Nano technology ?
Bob Reply
write examples of Nano molecule?
The nanotechnology is as new science, to scale nanometric
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
what school?
biomolecules are e building blocks of every organics and inorganic materials.
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
sciencedirect big data base
Introduction about quantum dots in nanotechnology
Praveena Reply
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
Damian Reply
absolutely yes
how to know photocatalytic properties of tio2 nanoparticles...what to do now
Akash Reply
it is a goid question and i want to know the answer as well
characteristics of micro business
for teaching engĺish at school how nano technology help us
Do somebody tell me a best nano engineering book for beginners?
s. Reply
there is no specific books for beginners but there is book called principle of nanotechnology
what is fullerene does it is used to make bukky balls
Devang Reply
are you nano engineer ?
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
what is the actual application of fullerenes nowadays?
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
what is the Synthesis, properties,and applications of carbon nano chemistry
Abhijith Reply
Mostly, they use nano carbon for electronics and for materials to be strengthened.
is Bucky paper clear?
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
so some one know about replacing silicon atom with phosphorous in semiconductors device?
s. Reply
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Do you know which machine is used to that process?
how to fabricate graphene ink ?
for screen printed electrodes ?
What is lattice structure?
s. Reply
of graphene you mean?
or in general
in general
Graphene has a hexagonal structure
On having this app for quite a bit time, Haven't realised there's a chat room in it.
how did you get the value of 2000N.What calculations are needed to arrive at it
Smarajit Reply
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