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What Does Your User Agent Say About You?

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A user agent is a computer program representing a person, for example, a browser in a Web context.

Besides a browser, a user agent could be a bot scraping webpages, a download manager, or another app accessing the Web. Along with each request they make to the server, browsers include a self-identifying User-Agent HTTP header called a user agent (UA) string. This string often identifies the browser, its version number, and its host operating system.

Spam bots, download managers, and some browsers often send a fake UA string to announce themselves as a different client. This is known as user agent spoofing.

The user agent string can be accessed with JavaScript on the client side using the navigator.userAgent property.

A typical user agent string looks like this: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:35.0) Gecko/20100101 Firefox/35.0".

(Source: Mozilla.org)

User Agent String

Browser Data

User Agent Css

author
David Lawrence
• Thursday, 15 October, 2020
• 13 min read

Peter Mortensen 27.2k2121 gold badges9393 silver badges123123 bronze badges Regarding the concept user agent style sheet”, consult section Cascade in the CSS 2.1 spec.

stylesheet css agent user fighting chrome google
(Source: stackoverflow.com)

Contents

They are just the rock bottom: in the absence of any style sheets provided by the page or by the user, the browser still has to render the content somehow, and the user agent style sheet just describes this. Marking the document as HTML5 by the proper doc type on the first line, solved my issue.

In order to present the page in a way that satisfies ” general presentation expectations.” For example, a default style sheet would provide base styles for things like font size, borders, and spacing between elements. It is common to employ a reset style sheet to deal with inconsistencies amongst browsers.

An useragent's default style sheet should present the elements of the document language in ways that satisfy general presentation expectations for the document language. For more information about user agents in general, see user agent.

Peter Mortensen 27.2k2121 gold badges9393 silver badges123123 bronze badges Define the values that you don't want to be used from Chrome's user agent style in your own CSS content.

Peter Mortensen 27.2k2121 gold badges9393 silver badges123123 bronze badges It was quite annoying but then I figured out as most of the people said, it's a markup error.

(Source: ru.stackoverflow.com)

I had a dumb error where a button element didn't look right in Chrome. I had partially styled it because I didn't want it to look like a traditional button.

Peter Mortensen 27.2k2121 gold badges9393 silver badges123123 bronze badges In Chrome developer tools, it says user agent stylesheet in place of the CSS file name.

CSS takes care of default formatting of documents through the concept of user agent style sheets, a cornerstone of the cascade. It means that a web browser doesn’t just present a line of text when it’s fed with an HTML document that has no styling information attached, but instead serves it using minimal formatting.

The following is a list of default style sheets I’ve compiled over recent years (except for Safari; thank you, Martin). Due to the fact that Fire bird, Firefox, and Co. are all based on the same layout engine, they’re quite similar, if not identical.

In Google Chrome, go to URL about:version and take note of the “profile path”. Browse to the profile path in your file browser.

button agent border chrome focus showing state google
(Source: stackoverflow.com)

Inside User StyleSheets”, there should be a file called Custom. In General section, check or uncheck “Show user agent styles”.

The major difference is that: CSS resets aim to remove all built-in browser styling. Elements like H1-6 will appear bold, larger etcetera consistently across browsers.

Press Command + Shift + P (Mac) or Control + Shift + P (Windows, Linux, Chrome OS) to open the Command Menu. In the User agent section disable the Select automatically checkbox.

Create a CSS class that selects the input directly, for example. Explicitly setting inheritance behavior for the cursor style on all inputs.

Because you have not specified values for the table element’s box, the default styles have been applied. In computing, an user agent is software (a software agent) that is acting on behalf of a user, such as a web browser that “retrieves, renders and facilitates end user interaction with Web content”.

border focus state button agent chrome showing google applied dev checked tool found
(Source: stackoverflow.com)

In case you didn’t know, every browser has its own default ‘ user agent stylesheet, that it uses to make styled websites appear more legible. I'm developing a website and trying to debug in Chrome dev tool.

On Chrome dev tool it says Sergeant style instead of CSS file. In order to present the page in a way that satisfies ” general presentation expectations.” For example, a default style sheet would provide base styles for things like font size, borders, and spacing between elements.

It is common to employ a reset style sheet to deal with inconsistencies among browsers. For this create CSS class and override the agent style sheet.

The cascade is an algorithm that defines how to combine property values originating from different sources. It lies at the core of CSS, as emphasized by the name: Cascading Style Sheets.

Though style sheets come from these different origins, they overlap in scope; to make this work, the cascade algorithm defines how they interact. Some browsers use actual style sheets for this purpose, while others simulate them in code, but the end result is the same.

css chrome window concepts basic overriding developer agent tools user styles web bioinformatics development figure
(Source: www.cellbiol.com)

The cascading algorithm determines how to find the value to apply for each property for each document element. That means rules whose selector matches the given element and which are part of an appropriate media at-rule.

A very simple introduction to the CSS cascade CSS Key Concepts: CSS syntax, at-rule, comments, specificity and inheritance, the box, layout modes and visual formatting models, and margin collapsing, or the initial, computed, resolved, specified, used, and actual values. Definitions of value syntax, shorthand properties and replaced elements.

By freezing it, it will be less useful over time in detecting the browser/platform/version, although the quoted reason for doing it is more about privacy and stopping fingerprinting rather than developer concerns. The main problem is that so many sites get it wrong, and the changes they make with that information ends up hurting more than it helps.

Functionality based on device detection is critical, widespread and not only in front end code. Huge software systems with backend code rely on device detection, as well as entire infrastructure stacks.

We use a Rails gem called Browser that exposes UA-derived info in a nice API. In the past it’s been kinda tricky to relay front-end information back to the server in such a way that’s useful on the first page load (since the UA doesn’t know stuff like viewport size).

(Source: www.crifan.com)

I remember some pretties fancy dancing I’ve done where I load up a skeleton page that executes a tiny bit of JavaScript that did things like measure the viewport width and screen size, then set a cookie and force-refreshed the page. If the cookie was present, the server had what it needed and didn’t load the skeleton page at all on those requests.

Tricky stuff, but then the server has information about the viewport width on the server-side, which is useful for things, like sending small-screen assets (e.g.different HTML), which was otherwise impossible. I would like to modify Chrome's user agent stylesheet.

I want to modify the default values and add some new rules that would help me speed up my workflow and enhance my browsing experience. In Google Chrome, go to URL about:version and take note of the “profile path”.

Change the background color of the element to “light blue” when the browser window is 600px wide or less: Using media queries are a popular technique for delivering a tailored style sheet (responsive web design) to desktops, laptops, tablets, and mobile phones.

Media features provide more specific details to media queries, by allowing to test for a specific feature of the user agent or display device. For example, you can apply styles to only those screens that are greater, or smaller, than a certain width.

(Source: book.techelevator.com)

The numbers in the table specifies the first browser version that fully supports the media rule. Not: The not keyword reverts the meaning of an entire media query.

Try it Yourself Media queries can also be used to change layout of a page depending on the orientation of the browser. You can have a set of CSS properties that will only apply when the browser window is wider than its height, a so-called “Landscape” orientation.

The color-scheme CSS property and the corresponding meta tag allow developers to opt their pages in to the theme-specific defaults of the user agent stylesheet. One puzzle piece that was only mentioned briefly in the article is the color-scheme CSS property and the corresponding meta tag of the same name.

They both make your life as a developer easier by allowing you to opt your page in to theme-specific defaults of the user agent stylesheet, such as, for example, form controls, scroll bars, as well as CSS system colors. You can have a look at Chrome's (and Chromium's) UA stylesheet and compare it to Firefox's or Safari's (and WebKit's).

For example, they all make links blue, general text black, and background color white, but there are also important (and sometimes annoying) differences, for instance, how they style form controls. The default provided by the stylesheet changes based on whether dark mode is on or off.

user chrome sheet agent override css
(Source: stackoverflow.com)

To illustrate this, here is one such CSS rule using the :matches pseudo class and WebKit-internal variables like -apple-system-control-background, as well as the WebKit-internal preprocessor directive #if defined : UA stylesheets can use either their own proprietary or the standardized semantic system colors, to determine how HTML elements should be rendered by default.

The UA stylesheet then assigns the following CSS only once, and covers both light and dark mode. The color-scheme property defined therein allows an element to indicate which color schemes it is comfortable being rendered with.

+ Indicates that the element is aware of and can handle the listed color schemes, and expresses an ordered preference between them. Warning: Previously, the specification allowed an additional value light only that indicated that the element had to be rendered with a light color scheme if possible, even if the user's preference is for a different color scheme.

Authors should not use this value, and should instead ensure their page renders well with whatever color scheme the user prefers. Examples are scroll bars, spellcheck underlines, form controls, etc.

To aid user agents in rendering the page background with the desired color scheme immediately, a color-scheme value can also be provided in a element. Since both the meta tag and the CSS property (if applied to the :root element) eventually result in the same behavior, I always recommend specifying the color scheme via the meta tag, so the browser can adapt to the preferred scheme faster.

stylesheet override agent focus user devtools started link
(Source: stackoverflow.com)

While for absolute baseline pages no additional CSS rules are necessary, in the general case you should always combine color-scheme with prefers-color-scheme. For example, the proprietary WebKit CSS color -webkit-link, used by WebKit and Chrome for the classic link blue RGB(0,0,238), has an insufficient contrast ratio of 2.23:1 on a black background and fails both the Wag AA and the Wag AAA requirements.

The interplay of the color-scheme CSS property and the corresponding meta tag with the prefers-color-scheme user preference media feature may seem confusing at first. The inline CSS code on the page sets the element's background-color to Greensboro in the general case, and to darkslategray if the user prefers a dark color scheme according to the prefers-color-scheme user preference media feature.

There is no additional developer-provided CSS involved to change the paragraph text or the background color of the page. Note how the element's background-color changes based on whether dark mode is enabled, following the rules in the developer-provided inline stylesheet on the page.

Light mode: The computed values of the border-top-color and the border-bottom-color that are both set to Buttonhole in the user agent stylesheet are now RGBA(0, 0, 0, 0.847). Dark mode: The computed values of the border-top-color and the border-bottom-color that are both set to Buttonhole in the user agent stylesheet are now RGBA(255, 255, 255, 0.847).

You can see the effects of color-scheme applied to many HTML elements in a demo on Glitch. The color-scheme CSS property and the corresponding meta tag were implemented by Rune Lillesveen.

ie9 css originating agent sheet user styles explorer ie11 shown within ll below open
(Source: stackoverflow.com)

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06: Map User Agent To Web Browser
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Sources
1 www.developer.amazon.com - https://www.developer.amazon.com/docs/fire-tablets/ft-user-agent-strings.html
2 deviceatlas.com - https://deviceatlas.com/blog/list-of-user-agent-strings
3 developer.amazon.com - https://developer.amazon.com/fr/docs/fire-tablets/ft-user-agent-strings.html
4 docs.aws.amazon.com - https://docs.aws.amazon.com/silk/latest/developerguide/user-agent.html
5 stackoverflow.com - https://stackoverflow.com/questions/5341637/how-do-detect-android-tablets-in-general-useragent
6 www.whatismybrowser.com - https://www.whatismybrowser.com/detect/what-is-my-user-agent
7 www.androidpolice.com - https://www.androidpolice.com/tags/user-agent-string/
8 www.zytrax.com - https://www.zytrax.com/tech/web/msie-history.html
9 www.texsoft.it - http://www.texsoft.it/index.php