CSS At-rules

Common At-rules

@media (max-width: 600px) {
  .text { font-size: 12px; }
}

@import url('fonts.css');

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

@font-face {
  font-family: 'MyFont';
  src: url('font.woff2');
}

🔹 @media Queries (Responsive Design)

Use @media queries to adapt your website's layout and styles to different devices, screen sizes, and orientations. Target breakpoints based on content, not specific devices. Use min-width and max-width for screen size, orientation for portrait/landscape, and prefers-color-scheme for dark/light mode. Implement a mobile-first approach: style for small screens first, then enhance for larger ones. Media queries are essential for creating accessible, performant websites that work seamlessly across smartphones, tablets, and desktops.

/* Mobile First Approach */
.container {
    padding: 10px;
    font-size: 14px;
}

/* Tablet */
@media (min-width: 768px) {
    .container {
        padding: 20px;
        font-size: 16px;
    }
}

/* Desktop */
@media (min-width: 1024px) {
    .container {
        padding: 30px;
        font-size: 18px;
        max-width: 1200px;
        margin: 0 auto;
    }
}

/* Dark Mode */
@media (prefers-color-scheme: dark) {
    .container {
        background-color: #1f2937;
        color: #f9fafb;
    }
}

🔹 @keyframes Animations

Create complex, multi-step animations with @keyframes for full control over intermediate states. Define a keyframe rule: @keyframes slide { from { transform: translateX(0); } to { transform: translateX(100px); } }. Apply it with animation: slide 2s ease infinite;. You can specify percentages (0%, 50%) for detailed sequences. Control playback with animation-direction, iteration-count, and fill-mode. Use for loading indicators, entrance animations, or continuous effects. Always respect prefers-reduced-motion.

/* Bounce Animation */
@keyframes bounce {
    0%, 20%, 50%, 80%, 100% {
        transform: translateY(0);
    }
    40% {
        transform: translateY(-20px);
    }
    60% {
        transform: translateY(-10px);
    }
}

.bounce-element {
    animation: bounce 2s infinite;
    display: inline-block;
    padding: 15px 30px;
    background: #3b82f6;
    color: white;
    border-radius: 8px;
    cursor: pointer;
}

/* Fade In Animation */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.fade-in {
    animation: fadeIn 1s ease-out;
}

🔹 @supports (Feature Queries)

Feature queries check if a browser supports a specific CSS property or value, enabling conditional styling. The syntax @supports (property: value) { /* styles */ } applies enclosed styles only if the test passes. Use them to safely implement newer features like grid, aspect-ratio, or backdrop-filter without breaking layouts in older browsers. Combine with logical operators (and, or, not) for complex detection. This is a cornerstone of progressive enhancement and resilient CSS.

/* Check for Grid support */
@supports (display: grid) {
    .grid-layout {
        display: grid;
        grid-template-columns: repeat(3, 1fr);
        gap: 1rem;
    }
}

/* Fallback for older browsers */
@supports not (display: grid) {
    .grid-layout {
        display: flex;
        flex-wrap: wrap;
    }
    .grid-layout > * {
        flex: 1 1 300px;
        margin: 0.5rem;
    }
}

/* Check for CSS custom properties */
@supports (--custom: property) {
    .modern-component {
        --primary: #3b82f6;
        --secondary: #10b981;
        background: var(--primary);
    }
}

🔹 @layer (Cascade Layers)

Cascade layers (@layer) allow you to define explicit precedence for your CSS rules, controlling the cascade order. Declare layers like @layer base, components, utilities;. Rules in later layers have priority over earlier ones, regardless of specificity. This prevents specificity wars and makes CSS easier to manage, especially in large projects or with third-party stylesheets. Layers help organize code into logical groups (reset, frameworks, themes, utilities) and provide a powerful tool for scalable, maintainable architecture.

/* Define layer order */
@layer reset, base, components, utilities;

/* Reset layer */
@layer reset {
    * {
        margin: 0;
        padding: 0;
        box-sizing: border-box;
    }
}

/* Base styles */
@layer base {
    body {
        font-family: system-ui, sans-serif;
        line-height: 1.6;
    }
}

/* Component styles */
@layer components {
    .button {
        padding: 0.5rem 1rem;
        border: none;
        border-radius: 0.25rem;
        background: #3b82f6;
        color: white;
        cursor: pointer;
    }
}

/* Utility classes */
@layer utilities {
    .text-center { text-align: center; }
    .mt-4 { margin-top: 1rem; }
}