Explanation: The <video> element is used for embedding video content in HTML5 web pages.

Explanation: The <!DOCTYPE> declaration specifies the version of HTML that a document follows and can affect how browsers interpret the content.

Explanation: Polyfills are used to provide support for modern web features in older browsers that may not natively support those features.

Explanation: The user agent is a software component within a web browser that requests and displays web content.

Explanation: The User-Agent String is sent by the user's browser to web servers and contains information about the browser and device being used.

Explanation: CSS reset or normalize.css is used to normalize default styles across browsers, reducing inconsistencies.

Explanation: Graceful degradation ensures that a website still functions, albeit with reduced features, in browsers that may not support certain technologies or styles.

Explanation: The navigator.userAgent property can be used to access information about the user's browser, including its name and version.

Explanation: Linux is an operating system, not a web browser. Common web browsers include Chrome, Firefox, Safari, and others.

Explanation: The color property in CSS is used to specify the color of text on a web page.

Explanation: Using feature detection, polyfills, and thorough testing across multiple browsers can help improve Cross-Browser Compatibility.

Explanation: Cross-browser compatibility issues can lead to web pages rendering differently or incorrectly on various browsers.

Explanation: Cross-browser compatibility ensures that a website functions well for users of different web browsers, increasing accessibility and user satisfaction.

Explanation: The Acid tests are developed by the World Wide Web Consortium (W3C) to assess web browser compatibility with web standards.

Explanation: jQuery is a widely used JavaScript library, but it is not specifically a polyfill library. Common polyfill libraries include "core-js" and "html5shiv."

Explanation: The transition property in CSS is commonly used to create smooth transitions and animations in web design.

Explanation: Cross-browser compatibility ensures that a website works as expected on various web browsers, such as Chrome, Firefox, Safari, and Internet Explorer.

Explanation: Vendor prefixes in CSS are used to apply browser-specific styles for features that are not yet standardized or experimental.

Explanation: The "viewport" meta tag is used to configure the viewport settings for responsive web design, controlling how web pages are displayed on different devices.

Explanation: The "Alt" attribute is used to provide alternative text for images, which is important for accessibility and search engine optimization (SEO).

Explanation: Feature testing is the process of testing website features to ensure they work as intended in all supported web browsers, improving Cross-Browser Compatibility.

Explanation: Feature detection in JavaScript allows developers to determine if a particular browser supports a specific feature before using it to avoid errors.

Explanation: Progressive enhancement is a web design strategy that involves starting with a baseline of essential functionality and then enhancing it for browsers that support advanced features.

Explanation: Modernizr is a JavaScript library used for feature detection, allowing developers to check if a browser supports specific HTML5 and CSS3 features.

Explanation: The box-sizing property allows developers to control whether an element's padding and border are included in its total width and height calculations.