CSS preprocessors and postprocessors

CSS preprocessors enhance development efficiency by extending CSS functionality, primarily through tools like Sass, Less, and Stylus. They support features such as variables, nesting, and mixins. The variable system allows reusable values for colors, fonts, etc. Nesting rules mirror HTML structure, reducing code duplication. Mixins function like reusable functions with parameter support. Post-processors like PostCSS optimize generated CSS, enabling features like autoprefixing and compression via plugins. Together, preprocessors handle authoring extensions while post-processors optimize compatibility. Modern CSS has gradually adopted features like variables and nesting, reducing reliance on preprocessors. However, deep nesting may impact performance, and build process complexity remains a consideration.

CSS Variables (Custom Properties)

CSS variables, a powerful feature introduced in CSS3, allow developers to define reusable values and reference them via variable names, enhancing code maintainability and flexibility. The basic syntax starts with two hyphens, and variables are typically defined globally in the `:root` pseudo-class. They are referenced using the `var()` function, with variable names being case-sensitive and supporting fallback values. Scoping is divided into global and local, following cascading rules where child elements inherit parent variable values, but同名 variables override. Dynamic features include JavaScript modification and media query responsiveness. Practical applications include theme switching, spacing system construction, and animation effects. Advanced techniques involve unit conversion calculations, chained references, and pseudo-element usage. Browser support is robust, but fallback solutions should be considered. Performance is excellent, though excessive use should be avoided, especially on low-performance devices.

Basics of media queries

Media queries are a technique in CSS3 used to apply different style rules based on device characteristics, enabling web pages to provide optimal display effects for different devices or screen sizes. They are a core tool for achieving responsive design. Media queries consist of media types and media features, supporting various logical operators such as `and` or `not`. Common media features include viewport width, device orientation, and resolution. In practical applications, following the mobile-first principle and setting reasonable breakpoints can achieve responsive navigation bars and grid layouts. Media queries can also be used in HTML via `<link>` or `<style>` tags. Modern responsive design practices include mobile-first strategies, breakpoint selection, and responsive images. Common issues include media queries not working and viewport problems on mobile devices. Advanced techniques include detecting touch device support, dark mode compatibility, and reducing animations. Combining media queries with CSS variables can improve code maintainability. Performance considerations involve organizing CSS structure and avoiding overuse. In terms of browser compatibility, modern browsers support media queries well, while older versions of IE can use conditional comments for fallback solutions.

The visual formatting model translates this sentence into English.

The visual formatting model is the core mechanism in CSS that describes the layout and rendering of elements, treating each element as a rectangular box and arranging them according to specific rules. It primarily involves block-level boxes, inline-level boxes, and anonymous boxes. The containing block serves as the reference frame for calculating an element's position and dimensions. Block-level elements occupy the full width of their containing block, and vertically adjacent elements may experience margin collapsing. Inline-level elements share line space and do not occupy a full line exclusively. The visual formatting model provides three positioning schemes: normal flow, floats, and absolute positioning. Formatting contexts, including block formatting contexts and inline formatting contexts, determine how elements interact. The stacking order controls the z-axis display priority of elements. Modern extensions include Flexbox and Grid layouts. The browser rendering process involves parsing HTML and CSS, constructing the render tree, computing layout, and painting.

The definition of animation keyframes

The keyframe rule in CSS animations is the core of defining animation sequences. Through keyframes, you can precisely control the style states of an animation at different points in time. Keyframes consist of an animation name and a set of percentage-based selectors or `from`/`to` selectors. The basic syntax includes defining initial states, intermediate states, and end states. Keyframe selectors support various definition methods, such as two-state animations, multi-stage animations, and non-uniform time distributions. Within keyframes, any valid CSS property can be defined, but only animatable properties will produce effects. Multiple animations can be combined, and keyframes also support advanced features like repeated definitions and dynamic style calculations. Practical applications include loading animations, typewriter effects, and complex path animations. For performance optimization, it is recommended to prioritize `transform` and `opacity`. Modern browsers have good support for keyframes, but older versions require prefixes. JavaScript can dynamically create and modify keyframe rules.

Selecting the transition timing function

In CSS transition effects, the timing function controls the rate of property value changes. Preset functions include linear, ease, ease-in, ease-out, and ease-in-out, each corresponding to different motion scenarios. Developers can use cubic-bezier to customize Bézier curves for achieving complex effects like elasticity. The steps function can create discrete transitions, simulating frame-by-frame animations. For performance optimization, it is recommended to use will-change for expensive properties, shorten durations on mobile devices, and simplify functions. Different properties can apply different functions to achieve composite effects. Chrome DevTools supports real-time curve debugging and can simulate physical motion. To accommodate users with reduced motion preferences, use media queries for responsive adjustments.

Detailed configuration of transition properties

CSS transitions allow property values to change smoothly over time. The `transition` property controls which CSS properties should have transition effects, the duration, speed curve, and delay time. Transitions are commonly used in user interaction scenarios, such as hover, focus, or active state changes. A complete transition property consists of four sub-properties: - `transition-property`: Specifies which CSS properties to apply transitions to. - `transition-duration`: Defines the duration of the transition. - `transition-timing-function`: Sets the speed curve of the transition. - `transition-delay`: Sets the delay before the transition starts. These properties can be declared individually or in shorthand. - **`transition-property`**: Specifies which CSS properties will have transitions. It can be set to a specific property name (e.g., `width`, `opacity`), `all` (all transitionable properties), or `none` (no transitions). Not all CSS properties can be transitioned—typically, numeric properties (e.g., width, height, position, opacity) can, while discrete properties (e.g., `display`) cannot. - **`transition-duration`**: Defines how long the transition lasts, in seconds (`s`) or milliseconds (`ms`). - **`transition-timing-function`**: Defines the speed curve of the transition. Common values include: - `ease` (default: slow start, fast middle, slow end) - `linear` (constant speed) - `ease-in` (slow start) - `ease-out` (slow end) - `ease-in-out` (slow start and end) - `cubic-bezier(n,n,n,n)` (custom Bézier curve) - `steps()` (creates step-based transitions). - **`transition-delay`**: Defines the wait time before the transition starts. A negative delay makes the transition start immediately but from an intermediate state. Different properties can have different transition effects. Some properties, like `transform` and `opacity`, can leverage GPU acceleration. JavaScript can listen for transition events. Transitions can be combined with CSS animations and adjusted using media queries. **Performance optimizations for transitions:** - Avoid transitioning properties like `height` or `margin` that cause reflows. - Prefer `transform` and `opacity` (compositing layer properties). - Reduce the number of properties transitioning simultaneously. - Keep transition durations reasonably short. Transitions can also be applied to pseudo-elements and combined with CSS custom properties for dynamic effects. Transition properties follow CSS cascading rules but are not inherited. The `will-change` property can hint to the browser which properties will change, though modern browsers often don’t need it. For compatibility, vendor prefixes may still be considered. JavaScript can dynamically modify transition properties. SVG properties can also use transitions. **Limitations of transitions:** - Cannot control intermediate states—only defines start and end. - Requires a trigger (e.g., `hover`). - Some properties have poor transition performance. - Cannot create complex multi-stage animations. - Can be disabled in print media using `@media print`.

The basic usage of the transition property

The CSS `transition` property is a crucial tool for achieving smooth transitions between element states. By defining the transition duration, properties, and speed curve, it makes changes appear more natural and fluid. `transition` is a shorthand property that includes four sub-properties: the property to transition, duration, timing function, and delay. - `transition-property` specifies which CSS properties to apply the transition to, whether a single property, multiple properties, or all properties. - `transition-duration` sets the duration of the transition in seconds or milliseconds. - `transition-timing-function` controls the speed curve, such as linear, ease-in, ease-out, or a custom Bézier curve. - `transition-delay` defines the delay before the transition starts. `transition` can be combined with JavaScript to trigger transitions by changing classes or styles. For performance, it’s recommended to prioritize `opacity` and `transform` to avoid reflows. While `transition` is ideal for simple state changes, complex animations may require keyframe animations. Practical applications include navigation menus, button feedback, modal fade-ins/outs, form focus styles, and card hover effects. Modern browsers support it well, though older versions may require prefixes.

Control of background size

The `background-size` property in CSS is used to control the display size and proportion of background images. By specifying width and height or using keywords like `cover` and `contain`, flexible layout effects can be achieved. This property supports multiple background images, responsive design, and can work in conjunction with background positioning, gradient backgrounds, and more. In practical applications, attention must be paid to browser compatibility, performance optimization, and coordination with other CSS properties. By using `background-size` appropriately, background effects adaptable to different devices can be created, while avoiding common mistakes such as forgetting to set `no-repeat` or overlooking high-resolution adaptation. Mastering the techniques of `background-size` can significantly enhance the flexibility and visual appeal of web design.

Background blending mode

Background blending mode is an important feature in CSS3, used to control how background images and colors blend. It offers 16 blending modes, such as multiply, screen, overlay, etc., enabling diverse visual effects. It supports multiple background blending, mixing layers sequentially. Practical applications include creating duotone effects, adding texture overlays, and color masks, and can be combined with other CSS properties to achieve complex effects. However, performance issues should be considered, especially on mobile devices. Modern browsers generally support it, but older versions of IE and Edge are incompatible. Feature detection can be used to provide fallback solutions. Common issues include background colors not displaying and blending order confusion, which can be resolved by explicitly specifying blending modes. Creative applications include dynamic blending effects and responsive design. For debugging, developer tools can be used to adjust settings in real time, and effects can be tested step by step.