How to Create a Black Underline with Red Text Using CSS3?

User agent stylesheets are the default CSS styles that browsers automatically apply to ensure that HTML elements that have not added custom styles are still basic readable. They affect the initial appearance of the page, but there are differences between browsers, which may lead to inconsistent display. Developers often solve this problem by resetting or standardizing styles. Use the Developer Tools' Compute or Style panel to view the default styles. Common coverage operations include clearing inner and outer margins, modifying link underscores, adjusting title sizes and unifying button styles. Understanding user agent styles can help improve cross-browser consistency and enable precise layout control.

Backdrop-filter is used to apply visual effects to the content behind the elements. 1. Use backdrop-filter:blur(10px) and other syntax to achieve the frosted glass effect; 2. Supports multiple filter functions such as blur, brightness, contrast, etc. and can be superimposed; 3. It is often used in glass card design, and it is necessary to ensure that the elements overlap with the background; 4. Modern browsers have good support, and @supports can be used to provide downgrade solutions; 5. Avoid excessive blur values and frequent redrawing to optimize performance. This attribute only takes effect when there is content behind the elements.

First, use JavaScript to obtain the user system preferences and locally stored theme settings, and initialize the page theme; 1. The HTML structure contains a button to trigger topic switching; 2. CSS uses: root to define bright theme variables, .dark-mode class defines dark theme variables, and applies these variables through var(); 3. JavaScript detects prefers-color-scheme and reads localStorage to determine the initial theme; 4. Switch the dark-mode class on the html element when clicking the button, and saves the current state to localStorage; 5. All color changes are accompanied by 0.3 seconds transition animation to enhance the user

vw and vh units achieve responsive design by associating element sizes with viewport width and height; 1vw is equal to 1% of viewport width, and 1vh is equal to 1% of viewport height; commonly used in full screen area, responsive fonts and elastic spacing; 1. Use 100vh or better 100dvh in the full screen area to avoid the influence of the mobile browser address bar; 2. Responsive fonts can be limited with 5vw and combined with clamp (1.5rem, 3vw, 3rem) to limit the minimum and maximum size; 3. Elastic spacing such as width:80vw, margin:5vhauto, padding:2vh3vw, can make the layout adaptable; pay attention to mobile device compatibility, accessibility and fixed width content conflicts, and it is recommended to give priority to using dvh first;

Theaspect-ratioCSSpropertydefinesthewidth-to-heightratioofanelement,ensuringconsistentproportionsinresponsivedesigns.1.Itisapplieddirectlytoelementslikeimages,videos,orcontainersusingsyntaxsuchasaspect-ratio:16/9.2.Commonusecasesincludemaintainingres

The:emptypseudo-classselectselementswithnochildrenorcontent,includingspacesorcomments,soonlytrulyemptyelementslikematchit;1.Itcanhideemptycontainersbyusing:empty{display:none;}tocleanuplayouts;2.Itallowsaddingplaceholderstylingvia::beforeor::after,wh

To achieve CSS element overlap, you need to use positioning and z-index attributes. 1. Use position and z-index: Set elements to non-static positioning (such as absolute, relative, etc.), and control the stacking order through z-index, the larger the value, the higher the value. 2. Common positioning methods: absolute is used for precise layout, relative is used for relatively offset and overlap adjacent elements, fixed or sticky is used for fixed positioning of suspended layers. 3. Actual example: By setting the parent container position:relative, child element position:absolute and different z-index, the card overlap effect can be achieved.

Define@keyframesbouncewith0%,100%attranslateY(0)and50%attranslateY(-20px)tocreateabasicbounce.2.Applytheanimationtoanelementusinganimation:bounce0.6sease-in-outinfiniteforsmooth,continuousmotion.3.Forrealism,use@keyframesrealistic-bouncewithscale(1.1