CSS Background Property Syntax

by agrace 19. August 2007 06:18

One of the trickier forms of CSS syntax is that of background properties, especially when using the shorthand form. This post will focus on the background-image property. When used correctly, the background-image property will enable you to create visually superior websites. Many of today's top Web 2.0 sites use this property, often combined with a repeating gradient image that blends into a background color.

First, an overview of the complete set of background properties and some brief descriptions:

Property Description
background Shorthand to set all background properties
background-attachment Sets background image as fixed or scrolled
background-color Sets background color of element
background-image Sets an image as the background
background-position Sets starting position of background image
background-repeat Sets how background image is repeated

 

For a more detailed breakdown, please see the W3Schools website.

The background properties can be brought together into a single line of shorthand CSS. We do not need to specify all the property values; we can use any one or more of them as follows:

background
Values [background-attachment] || [background-color] || [background-image] || [background-position] || [background-repeat]

 

If you have two values for the background-position property, they must appear together. And if we use length or percentage values, they must appear as horizontal first and vertical second. As long as you have at least one value present, you can omit all the rest. Other than that, there isn't any restriction on the order or particular properties to be included. If you omit any property values, then their default values are applied automatically. So, the following two declarations render the same output:

body { background: white url(test.gif); }
body { background: white url(test.gif) top left repeat scroll; }

 

The page you are looking at had its left navigation and main content area colors set by using a single 780 X 5 pixel, vertically-repeating image. The following CSS was employed:

background: url(img/main.gif) repeat-y;

 

This shorthand syntax is faster to type and easier to use than the full version. Using background images is an incredibly powerful way to take control of the overall look of your website.

Tags:

CSS




I've often jokingly thought to myself that if I was ever pulled over by a member of the Californian constabulary using a speed detection radar gun, that I would demand to see the source code in court. I'm neither a lawyer nor a physicist, but my intuition tells me that machines used for measuring anything need to be calibrated correctly and frequently. In addition, they are driven by software. Hypothetically speaking, since I would never break the speed limit, just because a machine tells someone I'm speeding, that doesn't make it so. Software never makes mistakes, right?

On a similar note, the Minnesota Supreme Court recently ruled that the makers of the Intoxilyzer 5000EN Breathalyzer turn over the source code by August 17 to defense attorneys for use in a DUI case. Since this is not likely to happen, the guy will most likely walk free. Interestingly, it seems that the Intoxilyzer is based on the old Z-80 microprocessor from 1976. The software that runs the breathalyzer is 24K worth of sophistication. This would be funny if it wasn't so serious. Peek me, poke me, but don't send me to prison on the word of an antique games chip as an expert witness.

The gap between technology and some form of sensible, enforceable legislation continues to widen. And it's not just speed guns and breathalyzers. Recently, a spate of traffic light cameras have appeared in my local twin-city area. Some say that they solved local budget woes overnight with the almost $400 fine for busting a light. If you go before the court, they present nice shiny B+W pictures of your face and your license plate. "Yes, that's me and that's my car. But where's the picture of the traffic light your honor? It was as green as the fields of Ireland when I drove though it..."

Speaking of tickets, we have the speed monitored here by aircraft. If you end up in court as the result of a radio call from the pilot to the police officer, make sure the pilot is present in court along with the police officer when you cross-examine the witnesses ;-)




Most people are by now familiar with the typical usage of the Eval() and Bind() methods in a GridView. You can even use a format string with the Eval() method:

<%# Eval("[Email]", "mailto:{0}") %>

 

However, sometimes you may want to obfuscate an email address when displaying a contact link in a GridView. This example displays a databased contact link in the GridView only if there is an email address in the database for a particular business.

GridView Business Listing

 

When the column is read-only, the Eval() one-way binding method is the most appropriate choice:

 <ItemTemplate>
   <table cellpadding="5" cellspacing="10" >
   <tr>
     <td style="padding-left:10px;">
       <span class="formtext"><b><%# Eval("BizName")%></b></span><br />
       <span class="formtext">
         Address: <%# Eval("Street")%>,&#160;<%# Eval("City")%>
       </span><br />
       <span class="formtext">Phone: <%# Eval("Phone")%></span><br />
       <span class="formtext">
         Email: <%# BuildContactRequest((int)Eval("BizID"), (string)Eval("Email")) %>
       </span><br />
       <span class="formtext">Website:<a href='<%# Eval("BizURL") %>'
        target="_blank"> <%# Eval("BizURL") %></a></span><br />
     </td>
   </tr>
   </table>
 </ItemTemplate>

 // Code-behind: URL with query parameter is returned
 protected string BuildContactRequest(int bizId, string email)
 {
   string contactURL = "";

   // Check if email is blank
   if (email == "")
   {
     return "";
   }
   // Contruct the Contact URL with the BizID query parameter
   else
   {
     contactURL += "<a href=Contact.aspx?bizParam=" + bizId + ">Contact Us</a>";
     return contactURL;
   }
 }


When the user clicks on the "Contact Us" link, they are directed to a Contact form which displays the recipient business name and generates an email to that business's (confidential) email address.

Contact Form

 

The business ID is passed as a query parameter and used to retrieve the business email address:

  if (Request.QueryString["bizParam"] != null)
  {
    bizId = Convert.ToInt32(Request.QueryString["bizParam"]);
    DataSet ds = new DataSet();

    // Get email address from DB and store it in session state
    ds = mbidBiz.GetContactDetailsByBizID(bizId);

    contactLabel.Visible = true;
    contactLabel.Text = "Contact: " + ds.Tables[0].Rows[0]["BizName"].ToString();

    Session["Email"] = ds.Tables[0].Rows[0]["Email"].ToString();
  }


If security is a real concern, rather than passing a query parameter, you could alternatively store and retrieve it from session state. Many small businesses today do not have their own website and may be using personal email addresses. The above example is based on an actual website I developed recently. Enjoy!