A few months back, I found myself in a similar situation. Initially, dynamic CSS generated by a dedicated handler/servlet was the go-to solution for performance improvement. However, as time went on, we realized that creating a customized CSS file to override standard elements was more efficient:

<link rel="stylesheet" href="standard.css" />
<link rel="stylesheet" href="<%= customer_code %>/custom_style.css" />
...
<img scr="<%= customer_code %>/logo.png" />

Each custom CSS now has its own unique URL, allowing browser caching to come into play.

This approach will result in savings with every user request, including:

1. reduced traffic from database to application layer
2. decreased traffic from application layer to browser
3. less computing required at the application layer

I strongly support the idea of having users fill out a web form outlining their desired customizations.

To begin, identify which resources can be substituted and whether new resources can be introduced. It is important to find a suitable storage location for these resources; smaller items like logos may be fine in the database, but larger resources will require consideration of database size limitations.

Next, determine the level of customization you want to offer users: from simply changing colors to revamping entire styles. For basic color changes, variables can be defined in a CSS file and dynamically served with data pulled from the database. Consider creating a CSS file like "styles.asp" containing code similar to this:

.header_area {
  border: 1px solid <%=headerBorderColor%>;
  background-color:  <%=headerBGColor%>;
  foreground-color:  <%=headerFGColor%>;
}

(I used JSP syntax here, although the concept works similarly in ASP.)

Alternatively, provide users with the option to specify an entire stylesheet to either replace or supplement the default one. Store the complete stylesheet in the database and serve it via its unique URL (avoid embedding it within the page).

<link rel="stylesheet" href="default_styles.css">
<link rel="stylesheet" href="white_label_css.asp">

Ensure the cache headers and content type are correctly set for the CSS file if serving it through an ASP page.

If there are concerns about the content that users might input into the white_label_css file, limiting their options through a custom tool could be beneficial. This tool would generate the CSS based on user selections, storing it in the database. Instead of allowing direct uploads and storage, users would fill out a form detailing their desired customizations. This approach helps control which CSS rules/changes are permitted, though flexibility could be limited.

I am intrigued by the concept of utilizing dynamic CSS with an ASP.Net Handler...

<link rel="stylesheet" href="style.ashx" />

style.ashx

<!--WebHandler Language="C#" Class="StyleSheetHandler"-->

StyleSheetHandler.cs

public class StyleSheetHandler : IHttpHandler {
        public void ProcessRequest (HttpContext context)
        {   
            context.Response.ContentType = "text/css";
            context.Response.ContentEncoding = System.Text.Encoding.UTF8;

            string css = BuildCSSString(); //details of this function are omitted

            context.Response.Cache.SetExpires(DateTime.Now.AddSeconds(600));
            context.Response.Cache.SetCacheability(HttpCacheability.Public);
            context.Response.Write( css );
        }

        public bool IsReusable
        {
            get { return true; }
        }

}

The BuildCSSString() Function is responsible for generating the css code based on data stored in the database and returning it to customize the base style on the master page.

My approach to addressing this issue would involve inputting the customizable elements (such as colors and font sizes) into a table that is connected to the user.

The preferred logo/avatar for the user can be saved either in the database or as a file on the filesystem.

In my opinion, the effectiveness of allowing users to write their own CSS depends on their familiarity with coding. If they are experienced web developers or have a natural inclination towards it, giving them the option to write CSS could work well. However, if they aren't as skilled in this area, you may need to consider generating static CSS based on user input and storing it in the database. Alternatively, you can store the input values and dynamically generate CSS using a custom handler.

Using a custom handler allows for more flexibility, as you can easily substitute values within the CSS code without having to worry about specificity or declaration order to ensure proper overrides take place.

One way to harness the power of PHP is by creating dynamic CSS, allowing you to customize styles based on user data stored in a database.

To learn more about generating dynamic CSS using PHP, check out resources like this one or that one.

It seems like you're looking to streamline color and typography edits, but what about layout changes? If we assume only color and typography will be altered, we can simply append new style classes at the bottom of our existing CSS file to override the styles (careful with using !important as it may limit customization options for users).

These new classes could be condensed into a single line string and saved as a varchar, then linked/copied directly into the page during rendering. Some possible methods include:

1. Adding inline CSS
2. Creating a separate CSS file partition for generated files and having browsers reference that location (maybe through a softlink?)
3. Utilizing Ajax to fetch and update the CSS in the DOM dynamically

If layout changes are expected, things get trickier. Dealing with scripting and event-handling complexities makes me lean towards avoiding significant layout alterations.