Is There a Reason to Use Uppercase Letters for Hexadecimal CSS Color Values

Is there a reason to use uppercase letters for hexadecimal CSS color values?

I am not aware of any differences other than personal preference. Personally, I prefer lowercase since it's quicker to read, although in very short strings such as CSS color values, the benefit is probably negligible. Really, I think it's just because I think lowercase looks better.

Hexadecimal, however, is traditionally written in uppercase, so maybe I'm - strictly speaking - in the 'wrong'.

Which is better, #fff or #FFF?

Neither;

color: white;

In all seriousness, tho', it doesn't matter so long as it matches the general design of your site. (For example, SO or FB should use #FFF, while, say, Apple would use #fff. Matches the rounded corners better, you see?)

It is recommendable to type the color's name instead of its hex value in CSS?

I'll prefer the hex value since it is supported by all browsers and I can specify wide range of colors than the named colors.

Are there any cons to using color names in place of color codes in CSS?

Different browsers may not agree on what some color names mean. There are not names for all 16 million 24-bit colors. In fact there are only 17 W3C-standard color names. It's probably OK to use those.

Personally I use a templating system at build time to pre-process my CSS files, so that I can keep a standard set of site colors and refer to them by name. That way I get the best of both worlds: I know exactly what my RGB color values are, but I can use simpler names in the CSS.

(Of course, it's still not possible to know exactly how a color will look on a given user's browser.)

edit — in the 5 years since this answer was written, preprocessors like Less and Sass have become pretty common. Those provide some very sophisticated tools for managing colors (and many other things) in CSS sources.

How to tranform css hex to uppercase in vscode?

My basic alternative that I used is the idea of @rioV8, however I would prefer to use replace field instead of Transform to UpperCase, I think that would be more quick.

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I would like to provide this as answer because it's at least working.

In vscode find #(?:[0-9a-fA-F]{3}){1,2} using regular expression, and replace it with \U$0.

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Updated: how to auto transform after save

Follow this link: How to automatically run a "find and replace" after save?

CSS - RGB or HEX for color

I believe that it is mostly a matter of personal taste whether you should use RGB or HEX. Personally I use HEX, because it feels more convenient - it is easier to scan when reading the code and easier to copy from your preferred image editor. Also for colors like white (#fff), black (#000) it could save you a few bytes (not that it would make much difference though).

In the end it is really just two different representations of the same thing, and from a performance perspective I don't think it matters. At least there are loads of other things you can do to increase performance, that will have a greater impact on performance.

How does hexadecimal color work?

Hexadecimal uses sixteen distinct symbols, in the case of css color the symbols 0–9 to represent values zero to nine (obviously), and A, B, C, D, E, F to represent values ten to fifteen. So, using one Hexadecimal character you can represent 16 values. With two Hexadecimal you can represent 256 (16*16) values.

In RGB you have colours represented by Red Green Blue (R=0-255, G=0-255, B=0-255), so we use 3 pairs of Hexadecimal symbols! So when you see an RGB color, you can make the calculation below.

Example:

Hex: #4C8ED5 is RGB: 76, 142, 213.

Because 4C = 76(Red), 8E = 142(Green), D5 = 213(Blue)!

Hope it helps your understanding!

More to read: Hexadecimal on Wikipedia and a nice RGB to Hexidecimal Converter

Performance differences between color declarations?

If we assume a modern browser making full use of the GPU then the internal color representation will be RGB floats. Ignoring the color name - which is probably just a map to hex anyway - I think that hex and channels will be the fastest. HSB will undoubtedly be the slowest, as the conversion from HSB to RGB does require some work - about 50 lines of C code.

However, I think that for the purpose of CSS, this is a completely irrelevant question. Even for HSB to RGB the amount of work on one color will be totally trivial. By way of support for this, I have several programs - including those running on mobiles - which do color manipulation at a per-pixel level on largish images where I am doing RGB->HSB->(some manipulation)->RGB. Even performing this operation 100,000 times on an ipad only results in a delay of a couple of seconds - so on this relatively slow platform, I think your typical worst case conversion can be safely assumed to take less then 0.0001 seconds. And that's being pessimistic.

So just use whatever is easiest to code.

ADDED: to support the don't worry about this option. Internally a GPU will manipulate colors as an array of floats, so in C terms

float color[4];

or something similar. So the only conversion being done for the numeric options is a simple divide by 255.

On the other hand conversion of HSB to RGB takes considerably longer - I'd estimate, from having written code to do it, about 10 to 20 operations. So in crude terms HSB is considerably slower, BUT 20 (or even 20,000) operations on a modern GPU isn't worth worrying about - it's imperceptible.

Are property values in CSS case-sensitive?

(updating @ÁlvaroG.Vicario answer and comments, and complementing this answer... This is a Wiki, please edit to enhance)

Example: for CSS3 (and HTML5) there are new explicit rules, as "font-face property must be case-insensitive".[2]

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Context

W3C interoperating standards, mainly XML, HTML, CSV and CSS.

CSS general rules

CSS2 (a W3C standard of 2008) fixed basic conventions about "Characters and case", and CSS3 (a W3C standard for 2015) added something more.

1. By default "all CSS syntax is case-insensitive (...)" [1]

2. There are exceptions, "(...) except for parts that are not under the control of CSS"[1]

2.1. element names are case-sensitive in HTML5 (?) and XML, but case-insensitive in HTML4.

2.2. identifiers (including element names, classes, and IDs in selectors) are case-sensitive. HTML attributes id and class, of font names, and of URIs lies outside the scope of the CSS specification.

3. ....

4. The

Case matrix

Exceptions and specific (explicited in a reference) rules. "YES" indicate that value is case-sensitive.

Property values:

 CSS property      | Case-sens. | Reference and notes
 ------------------|------------|--------------------
 %colorVals        | NO         | [3]
 font-family       | NO         | [2]
 %url              | YES        | ...
 content           | YES        | ...
 ----------------------------------------------------
 %colorVals = color, background, etc.
 %url = background-image, etc. that use `url()`, see [7] and notes. 

Selector values:

 CSS selector      | Case-sens. | Reference and notes
 ------------------|------------|--------------------
 id                | YES        |...
 element           | YES/NO     | ... YES for XML...
 class name        | YES        | [5]
 (`~ i` operator)  | NO         | [6]
 ----------------------------------------------------
 YES/NO = depends on the document language (see ref. and notes).

REFERENCES:

[1] W3C/CSS2/syndata, sec. 4.1.3 Characters and case.

[2] W3C/CSS3-fonts, sec. 5.1 Case sensitivity of font family names

[3] W3C/CSS3-color, sec. 4.1. Basic color keywords

[4] W3C/CSS3-values, sec. 3.1. Pre-defined Keywords

[5] W3C/Selectors, sec. 3. Case sensitivity

[6] W3C/Selectors4, sec. 6.3. Case-sensitivity

[7] RFC 3986 and URL syntax illustration at Wikipedia.

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Quotations and notes

• Typical URLs starts with domain, that is case insensitive, but after it (path, query or fragment syntatical components), is case sensitive. See [7].

• "User agents must match these names case insensitively". [2]

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