CSS Interview Questions And Answers _ 4

Started by ganeshbala, Mar 28, 2008, 05:40 PM

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CSS Interview Questions And Answers

How to use CSS to separate content and design ?
The idea here is that all sites contain two major parts, the content: all your articles, text and photos and the design: rounded corners, colors and effects. Usually those two are made in different parts of a webpage's lifetime. The design is determined at the beginning and then you start filling it with content and keep the design fixed.

In CSS you just add the nifty <link>-tag I've told you about to the head of your HTML document and you have created a link to your design. In the HTML document you put content only, and that link of yours makes sure it looks right. You can also use the exact same link on many of your pages, giving them all of them the same design. You want to add content? Just write a plain HTML document and think about marking things up like "header" instead of "big blue header" and use CSS to make all headers look the way you want!

Some examples of good and bad coding. What's wrong with this?
<font size="3">Welcome to my page</font>

Comment: The font-tag is design and design shouldn't be in the HTML document. All design should be in the CSS-file! Instead do this:

In the HTML:
<h1>Welcome to my page</h1>

In the CSS:
h1 { font-size: 2em; }

One more example:

An error occurred

This looks right doesn't it? But if you look up what stands for you quickly find bold. But bold is certainly design, so it still doesn't belong in the HTML document. A better choice is that stands for emphasis or simply "this piece of text is important". So instead of saying "this text looks like this" you are saying "this text is important" and you let the looks be decided by the CSS. Seems like a minor change, but it illustrates how to select your tags. Use this instead:

In the HTML:
An error occured

In the CSS:
em {
font-weight: bold;
color: Red;

One last example:

<tr><td><a href="">first link[/url]</td></tr>
<tr><td><a href="">second link[/url]</td></tr>

>Can CSS be used with other than HTML documents?
Yes. CSS can be used with any ny structured document format. e.g. XML, however, the method of linking CSS with other document types has not been decided yet.

Can Style Sheets and HTML stylistic elements be used in the same document?
Yes. Style Sheets will be ignored in browsers without CSS-support and HTML stylistic elements used.

What are pseudo-classes?
Pseudo-classes are fictional element types that do not exist in HTML. In CSS1 there is only one element type which can be classed this way, namely the A element (anchor). By creating three fictional types of the A element individual style can be attached to each class. These three fictional element types are: A as unvisited link, A as active link and A as visited link. Pseudo-classes are created by a colon followed by pseudo-class's name. They can also be combined with normal classes, e.g.:

A:link {background: black; color: white}
A:active {background: black; color: red}
A:visited {background: transparent; color: black}

<A HREF....>This anchor (or rather these anchors) will be displayed as declared above[/url]

A.foot:link {background: black; color: white}
A.foft:active {background; black: color: red}
A.foot:visited {background: transparent; color: black}

<A CLASS=foot HREF....>This anchor and all other anchors with CLASS foot will be displayed as declared above[/url]

How do I design for backward compatibility using Style Sheets?
Existing HTML style methods (such as <font SIZE> and ) may be easily combined with style sheet specification methods. Browsers that do not understand style sheets will use the older HTML formatting methods, and style sheets specifications can control the appearance of these elements in browsers that support CSS1.

As a reader, how can I make my browser recognize my own style sheet?
It is not possible to do this in Netscape yet (as of version 4.0.)
Internet Explorer 3.0 (Win95/NT)
>[It is possible to do this at least in Windows95/NT, but no user interface is provided. Unknown how this might be accomplished on other operating systems.]

1. Open the Registry editor (Start..Run..regedit..ENTER)
2. Under the 'HKEY_LOCAL_MACHINE\Software\Microsoft\InternetExplorer\Styles' key, Edit..New..String Value
3. The new value should be called 'StyleSheet Pathname'
4. For the value, type in the full directory path of your .css style sheet.

Internet Explorer 4.0 (Win95/NT)

1. Under the View menu, select 'Internet Options'.
2. Under the 'General' tab, choose the 'Accessibility' button.
3. Choose the 'Format documents using my style sheet' check box and 'Browse...' to the location of your .css style sheet.

How do I get rid of the gap under my image?
Images are inline elements, which means they are treated in the same way as text. Most people kind of know this - they know that if you use 'text-align:center' on an image it will be centred. What many people don't realise is that this means you will have a gap underneath an image. This gap is for the descenders of letters like j,q,p,y and g. To get rid of this gap you need to make the image block-level - like this :

img {display:block;}

One problem that this can cause is when you want to have a few images next to each other - if they are block-level, they won't be next to each other. To get around that, you can use float:left. Of course, this might present another problem - maybe you don't want the image to float left. In this case, you can use an unordered list like this :

ul, li {
margin:0 auto;
ul {
li {
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>
<li><img src="wine.jpg" height="50" width="50" alt="wine" /></li>

Why use Style Sheets?
Style sheets allow a much greater degree of layout and display control than has ever been possible thus far in HTML. The amount of format coding necessary to control display characteristics can be greatly reduced through the use of external style sheets which can be used by a group of documents. Also, multiple style sheets can be integrated from different sources to form a cohesive tapestry of styles for a document. Style sheets are also backward compatible - They can be mixed with HTML styling elements and attributes so that older browsers can view content as intended.

What does the "Cascading" in "Cascading Style Sheets" mean?
Style Sheets allow style information to be specified from many locations. Multiple (partial) external style sheets can be referenced to reduce redundancy, and both authors as well as readers can specify style preferences. In addition, three main methods can be employed by an author to add style information to HTML documents, and multiple approaches for style control are available in each of these methods. In the end, style can be specified for a single element using any, or all, of these methods. What style is to be used when there is a direct conflict between style specifications for an element?
Cascading comes to the rescue. A document can have styles specified using all of these methods, but all the information will be reduced to a single, cohesive "virtual" Style Sheet. Conflict resolution is based on each style rule having an assigned weight according to its importance in the scheme of things. A rule with a higher overall importance will carry a higher weight. This will be used in place of a competing style rule with a lower weight/importance. A hierarchy of competing styles is thus formed creating a "cascade" of styles according to their assigned weights. The algorithm used to determine this cascading weight scale is fairly complex.

What is CSS rule 'at-rule'?
There are two types of CSS rules: ruleset and at-rule. At-rule is a rule that applies to the whole style sheet and not to a specific selector only (like in ruleset). They all begin with the @ symbol followed by a keyword made up of letters a-z, A-Z, digits 0-9, dashes and escaped characters, e.g. @import or @font-face.

What is selector?
CSS selector is equivalent of HTML element(s). It is a string identifying to which element(s) the corresponding declaration(s) will apply and as such the link between the HTML document and the style sheet.
For example in P {text-indent: 10pt} the selector is P and is called type selector as it matches all instances of this element type in the document.
in P, UL {text-indent: 10pt} the selector is P and UL (see grouping); in .class {text-indent: 10pt} the selector is .class (see class selector).

What is CLASS selector?
Class selector is a "stand alone" class to which a specific style is declared. Using the CLASS attribute the declared style can then be associated with any HTML element. The class selectors are created by a period followed by the class's name. The name can contain characters a-z, A-Z, digits 0-9, period, hyphen, escaped characters, Unicode characters 161-255, as well as any Unicode character as a numeric code, however, they cannot start with a dash or a digit. (Note: in HTML the value of the CLASS attribute can contain more characters).It is a good practice to name classes according to their function than their appearance.

.footnote {font: 70%} /* class as selector */

<ADDRESS CLASS=footnote/>This element is associated with the CLASS footnote</ADDRESS>
<P CLASS=footnote>And so is this</P>

What is CSS declaration?
CSS declaration is style attached to a specific selector. It consists of two parts; property which is equivalent of HTML attribute, e.g. text-indent: and value which is equivalent of HTML value, e.g. 10pt. NOTE: properties are always ended with a colon.

What is 'important' declaration?
Important declaration is a declaration with increased weight. Declaration with increased weight will override declarations with normal weight. If both reader's and author's style sheet contain statements with important declarations the author's declaration will override the reader's.

BODY {background: white ! important; color: black}

In the example above the background property has increased weight while the color property has normal.

What is cascade?
Cascade is a method of defining the weight (importance) of individual styling rules thus allowing conflicting rules to be sorted out should such rules apply to the same selector.

Declarations with increased weight take precedence over declaration with normal weight:

P {color: white ! important} /* increased weight */
P (color: black} /* normal weight */

Are Style Sheets case sensitive?
No. Style sheets are case insensitive. Whatever is case insensitive in HTML is also case insensitive in CSS. However, parts that are not under control of CSS like font family names and URLs can be case sensitive - IMAGE.gif and image.gif is not the same file.

How do I have a non-tiling (non-repeating) background image?
With CSS, you can use the background-repeat property. The background repeat can be included in the shorthand background property, as in this example:

body {
background: white url(example.gif) no-repeat ;
color: black ;

CSS is clearly very useful for separating style from content. But apparently people tend to have problems when using it for layouts. Would you say this is because people have not yet understood how to properly do layout in CSS, or is it CSS that is lacking in this area? What can be done to improve the situation? --- Would the web benefit from HTML and CSS being complemented with some kind of "layout language"?
Layout and style should be tackled by the same language and the two are intertwined. Trying to split the two is like splitting the HTML specification in two, one specification describing inline elements and the other describing block elements. It's not worth the effort. CSS is capable of describing beautiful and scalable layouts. The CSS Zen Garden has been a eye-opening showcase of what is possible today. If MS IE had supported CSS tables, another set of layouts would have been possible. So, there is still lots of potential in the existing CSS specifications which should be the next milestone.

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