new skill web-coder (#881)

* new skill web-coder * codespellrc: add aNULL HTTPS config cipher string * Apply suggestions from code review Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com> * Apply suggestions from code review * Apply suggestion from @jhauga --------- Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
2026-03-13 04:35:12 +00:00 · 2026-03-05 05:43:04 -05:00
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+# CSS & Styling Reference
+
+Comprehensive reference for Cascading Style Sheets, layout systems, and modern styling techniques.
+
+## Core Concepts
+
+### CSS (Cascading Style Sheets)
+
+Style sheet language used for describing the presentation of HTML documents.
+
+**Three Ways to Apply CSS**:
+
+1. **Inline**: `<div style="color: blue;">`
+2. **Internal**: `<style>` tag in HTML
+3. **External**: Separate `.css` file (recommended)
+
+### The Cascade
+
+The algorithm that determines which CSS rules apply when multiple rules target the same element.
+
+**Priority Order** (highest to lowest):
+
+1. Inline styles
+2. ID selectors (`#id`)
+3. Class selectors (`.class`), attribute selectors, pseudo-classes
+4. Element selectors (`div`, `p`)
+5. Inherited properties
+
+**Important**: `!important` declaration overrides normal specificity (use sparingly)
+
+### CSS Selectors
+
+| Selector | Example | Description |
+|----------|---------|-------------|
+| Element | `p` | Selects all `<p>` elements |
+| Class | `.button` | Selects elements with `class="button"` |
+| ID | `#header` | Selects element with `id="header"` |
+| Universal | `*` | Selects all elements |
+| Descendant | `div p` | `<p>` inside `<div>` (any level) |
+| Child | `div > p` | Direct child `<p>` of `<div>` |
+| Adjacent Sibling | `h1 + p` | `<p>` immediately after `<h1>` |
+| General Sibling | `h1 ~ p` | All `<p>` siblings after `<h1>` |
+| Attribute | `[type="text"]` | Elements with specific attribute |
+| Attribute Contains | `[href*="example"]` | Contains substring |
+| Attribute Starts | `[href^="https"]` | Starts with string |
+| Attribute Ends | `[href$=".pdf"]` | Ends with string |
+
+### Pseudo-Classes
+
+Target elements based on state or position:
+
+```css
+/* Link states */
+a:link { color: blue; }
+a:visited { color: purple; }
+a:hover { color: red; }
+a:active { color: orange; }
+a:focus { outline: 2px solid blue; }
+
+/* Structural */
+li:first-child { font-weight: bold; }
+li:last-child { border-bottom: none; }
+li:nth-child(odd) { background: #f0f0f0; }
+li:nth-child(3n) { color: red; }
+p:not(.special) { color: gray; }
+
+/* Form states */
+input:required { border-color: red; }
+input:valid { border-color: green; }
+input:invalid { border-color: red; }
+input:disabled { opacity: 0.5; }
+input:checked + label { font-weight: bold; }
+```
+
+### Pseudo-Elements
+
+Style specific parts of elements:
+
+```css
+/* First line/letter */
+p::first-line { font-weight: bold; }
+p::first-letter { font-size: 2em; }
+
+/* Generated content */
+.quote::before { content: '"'; }
+.quote::after { content: '"'; }
+
+/* Selection */
+::selection { background: yellow; color: black; }
+
+/* Placeholder */
+input::placeholder { color: #999; }
+```
+
+## Box Model
+
+Every element is a rectangular box with:
+
+1. **Content**: The actual content (text, images)
+2. **Padding**: Space around content, inside border
+3. **Border**: Line around padding
+4. **Margin**: Space outside border
+
+```css
+.box {
+  /* Content size */
+  width: 300px;
+  height: 200px;
+  
+  /* Padding */
+  padding: 20px; /* All sides */
+  padding: 10px 20px; /* Vertical | Horizontal */
+  padding: 10px 20px 15px 25px; /* Top | Right | Bottom | Left */
+  
+  /* Border */
+  border: 2px solid #333;
+  border-radius: 8px;
+  
+  /* Margin */
+  margin: 20px auto; /* Vertical | Horizontal (auto centers) */
+  
+  /* Box-sizing changes how width/height work */
+  box-sizing: border-box; /* Include padding/border in width/height */
+}
+```
+
+## Layout Systems
+
+### Flexbox
+
+One-dimensional layout system (row or column):
+
+```css
+.container {
+  display: flex;
+  
+  /* Direction */
+  flex-direction: row; /* row | row-reverse | column | column-reverse */
+  
+  /* Wrapping */
+  flex-wrap: wrap; /* nowrap | wrap | wrap-reverse */
+  
+  /* Main axis alignment */
+  justify-content: center; /* flex-start | flex-end | center | space-between | space-around | space-evenly */
+  
+  /* Cross axis alignment */
+  align-items: center; /* flex-start | flex-end | center | stretch | baseline */
+  
+  /* Multi-line cross axis */
+  align-content: center; /* flex-start | flex-end | center | space-between | space-around | stretch */
+  
+  /* Gap between items */
+  gap: 1rem;
+}
+
+.item {
+  /* Grow factor */
+  flex-grow: 1; /* Takes available space */
+  
+  /* Shrink factor */
+  flex-shrink: 1; /* Can shrink if needed */
+  
+  /* Base size */
+  flex-basis: 200px; /* Initial size before growing/shrinking */
+  
+  /* Shorthand */
+  flex: 1 1 200px; /* grow | shrink | basis */
+  
+  /* Individual alignment */
+  align-self: flex-end; /* Overrides container's align-items */
+  
+  /* Order */
+  order: 2; /* Change visual order (default: 0) */
+}
+```
+
+### CSS Grid
+
+Two-dimensional layout system (rows and columns):
+
+```css
+.container {
+  display: grid;
+  
+  /* Define columns */
+  grid-template-columns: 200px 1fr 1fr; /* Fixed | Flexible | Flexible */
+  grid-template-columns: repeat(3, 1fr); /* Three equal columns */
+  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr)); /* Responsive */
+  
+  /* Define rows */
+  grid-template-rows: 100px auto 50px; /* Fixed | Auto | Fixed */
+  
+  /* Named areas */
+  grid-template-areas:
+    "header header header"
+    "sidebar main main"
+    "footer footer footer";
+  
+  /* Gap between cells */
+  gap: 1rem; /* Row and column gap */
+  row-gap: 1rem;
+  column-gap: 2rem;
+  
+  /* Alignment */
+  justify-items: start; /* Align items horizontally within cells */
+  align-items: start; /* Align items vertically within cells */
+  justify-content: center; /* Align grid within container horizontally */
+  align-content: center; /* Align grid within container vertically */
+}
+
+.item {
+  /* Span columns */
+  grid-column: 1 / 3; /* Start / End */
+  grid-column: span 2; /* Span 2 columns */
+  
+  /* Span rows */
+  grid-row: 1 / 3;
+  grid-row: span 2;
+  
+  /* Named area */
+  grid-area: header;
+  
+  /* Individual alignment */
+  justify-self: center; /* Horizontal alignment */
+  align-self: center; /* Vertical alignment */
+}
+```
+
+### Grid vs Flexbox
+
+| Use Case | Best Choice |
+|----------|-------------|
+| One-dimensional layout (row or column) | Flexbox |
+| Two-dimensional layout (rows and columns) | Grid |
+| Align items along one axis | Flexbox |
+| Create complex page layouts | Grid |
+| Distribute space between items | Flexbox |
+| Precise control over rows and columns | Grid |
+| Content-first responsive design | Flexbox |
+| Layout-first responsive design | Grid |
+
+## Positioning
+
+### Position Types
+
+```css
+/* Static (default) - normal flow */
+.static { position: static; }
+
+/* Relative - offset from normal position */
+.relative {
+  position: relative;
+  top: 10px; /* Move down 10px */
+  left: 20px; /* Move right 20px */
+}
+
+/* Absolute - removed from flow, positioned relative to nearest positioned ancestor */
+.absolute {
+  position: absolute;
+  top: 0;
+  right: 0;
+}
+
+/* Fixed - removed from flow, positioned relative to viewport */
+.fixed {
+  position: fixed;
+  bottom: 20px;
+  right: 20px;
+}
+
+/* Sticky - switches between relative and fixed based on scroll */
+.sticky {
+  position: sticky;
+  top: 0; /* Sticks to top when scrolling */
+}
+```
+
+### Inset Properties
+
+Shorthand for positioning:
+
+```css
+.element {
+  position: absolute;
+  inset: 0; /* All sides: top, right, bottom, left = 0 */
+  inset: 10px 20px; /* Vertical | Horizontal */
+  inset: 10px 20px 30px 40px; /* Top | Right | Bottom | Left */
+}
+```
+
+### Stacking Context
+
+Control layering with `z-index`:
+
+```css
+.behind { z-index: 1; }
+.ahead { z-index: 10; }
+.top { z-index: 100; }
+```
+
+**Note**: `z-index` only works on positioned elements (not `static`)
+
+## Responsive Design
+
+### Media Queries
+
+Apply styles based on device characteristics:
+
+```css
+/* Mobile-first approach */
+.container {
+  padding: 1rem;
+}
+
+/* Tablet and up */
+@media (min-width: 768px) {
+  .container {
+    padding: 2rem;
+    max-width: 1200px;
+    margin: 0 auto;
+  }
+}
+
+/* Desktop */
+@media (min-width: 1024px) {
+  .container {
+    padding: 3rem;
+  }
+}
+
+/* Landscape orientation */
+@media (orientation: landscape) {
+  .header { height: 60px; }
+}
+
+/* High-DPI screens */
+@media (min-resolution: 192dpi) {
+  .logo { background-image: url('logo@2x.png'); }
+}
+
+/* Dark mode preference */
+@media (prefers-color-scheme: dark) {
+  body {
+    background: #222;
+    color: #fff;
+  }
+}
+
+/* Reduced motion preference */
+@media (prefers-reduced-motion: reduce) {
+  * {
+    animation-duration: 0.01ms !important;
+    transition-duration: 0.01ms !important;
+  }
+}
+```
+
+### Responsive Units
+
+| Unit | Description | Example |
+|------|-------------|---------|
+| `px` | Pixels (absolute) | `16px` |
+| `em` | Relative to parent font-size | `1.5em` |
+| `rem` | Relative to root font-size | `1.5rem` |
+| `%` | Relative to parent | `50%` |
+| `vw` | Viewport width (1vw = 1% of viewport width) | `50vw` |
+| `vh` | Viewport height | `100vh` |
+| `vmin` | Smaller of vw or vh | `10vmin` |
+| `vmax` | Larger of vw or vh | `10vmax` |
+| `ch` | Width of "0" character | `40ch` |
+| `fr` | Fraction of available space (Grid only) | `1fr` |
+
+### Responsive Images
+
+```css
+img {
+  max-width: 100%;
+  height: auto;
+}
+
+/* Art direction with picture element */
+```
+
+```html
+<picture>
+  <source media="(min-width: 1024px)" srcset="large.jpg">
+  <source media="(min-width: 768px)" srcset="medium.jpg">
+  <img src="small.jpg" alt="Responsive image">
+</picture>
+```
+
+## Typography
+
+```css
+.text {
+  /* Font family */
+  font-family: 'Helvetica Neue', Arial, sans-serif;
+  
+  /* Font size */
+  font-size: 16px; /* Base size */
+  font-size: 1rem; /* Relative to root */
+  font-size: clamp(14px, 2vw, 20px); /* Responsive with min/max */
+  
+  /* Font weight */
+  font-weight: normal; /* 400 */
+  font-weight: bold; /* 700 */
+  font-weight: 300; /* Light */
+  
+  /* Font style */
+  font-style: italic;
+  
+  /* Line height */
+  line-height: 1.5; /* 1.5 times font-size */
+  line-height: 24px;
+  
+  /* Letter spacing */
+  letter-spacing: 0.05em;
+  
+  /* Text alignment */
+  text-align: left; /* left | right | center | justify */
+  
+  /* Text decoration */
+  text-decoration: underline;
+  text-decoration: none; /* Remove underline from links */
+  
+  /* Text transform */
+  text-transform: uppercase; /* uppercase | lowercase | capitalize */
+  
+  /* Word spacing */
+  word-spacing: 0.1em;
+  
+  /* White space handling */
+  white-space: nowrap; /* Don't wrap */
+  white-space: pre-wrap; /* Preserve whitespace, wrap lines */
+  
+  /* Text overflow */
+  overflow: hidden;
+  text-overflow: ellipsis; /* Show ... when text overflows */
+  
+  /* Word break */
+  word-wrap: break-word; /* Break long words */
+  overflow-wrap: break-word; /* Modern version */
+}
+```
+
+## Colors
+
+```css
+.colors {
+  /* Named colors */
+  color: red;
+  
+  /* Hex */
+  color: #ff0000; /* Red */
+  color: #f00; /* Shorthand */
+  color: #ff0000ff; /* With alpha */
+  
+  /* RGB */
+  color: rgb(255, 0, 0);
+  color: rgba(255, 0, 0, 0.5); /* With alpha */
+  color: rgb(255 0 0 / 0.5); /* Modern syntax */
+  
+  /* HSL (Hue, Saturation, Lightness) */
+  color: hsl(0, 100%, 50%); /* Red */
+  color: hsla(0, 100%, 50%, 0.5); /* With alpha */
+  color: hsl(0 100% 50% / 0.5); /* Modern syntax */
+  
+  /* Color keywords */
+  color: currentColor; /* Inherit color */
+  color: transparent;
+}
+```
+
+### CSS Color Space
+
+Modern color spaces for wider gamut:
+
+```css
+.modern-colors {
+  /* Display P3 (Apple devices) */
+  color: color(display-p3 1 0 0);
+  
+  /* Lab color space */
+  color: lab(50% 125 0);
+  
+  /* LCH color space */
+  color: lch(50% 125 0deg);
+}
+```
+
+## Animations and Transitions
+
+### Transitions
+
+Smooth changes between states:
+
+```css
+.button {
+  background: blue;
+  color: white;
+  transition: all 0.3s ease;
+  /* transition: property duration timing-function delay */
+}
+
+.button:hover {
+  background: darkblue;
+  transform: scale(1.05);
+}
+
+/* Individual properties */
+.element {
+  transition-property: opacity, transform;
+  transition-duration: 0.3s, 0.5s;
+  transition-timing-function: ease, ease-in-out;
+  transition-delay: 0s, 0.1s;
+}
+```
+
+### Keyframe Animations
+
+```css
+@keyframes fadeIn {
+  from {
+    opacity: 0;
+    transform: translateY(20px);
+  }
+  to {
+    opacity: 1;
+    transform: translateY(0);
+  }
+}
+
+.element {
+  animation: fadeIn 0.5s ease forwards;
+  /* animation: name duration timing-function delay iteration-count direction fill-mode */
+}
+
+/* Multiple keyframes */
+@keyframes slide {
+  0% { transform: translateX(0); }
+  50% { transform: translateX(100px); }
+  100% { transform: translateX(0); }
+}
+
+.slider {
+  animation: slide 2s infinite alternate;
+}
+```
+
+## Transforms
+
+```css
+.transform {
+  /* Translate (move) */
+  transform: translate(50px, 100px); /* X, Y */
+  transform: translateX(50px);
+  transform: translateY(100px);
+  
+  /* Rotate */
+  transform: rotate(45deg);
+  
+  /* Scale */
+  transform: scale(1.5); /* 150% size */
+  transform: scale(2, 0.5); /* X, Y different */
+  
+  /* Skew */
+  transform: skew(10deg, 5deg);
+  
+  /* Multiple transforms */
+  transform: translate(50px, 0) rotate(45deg) scale(1.2);
+  
+  /* 3D transforms */
+  transform: rotateX(45deg) rotateY(30deg);
+  transform: perspective(500px) translateZ(100px);
+}
+```
+
+## CSS Variables (Custom Properties)
+
+```css
+:root {
+  --primary-color: #007bff;
+  --secondary-color: #6c757d;
+  --spacing: 1rem;
+  --border-radius: 4px;
+}
+
+.element {
+  color: var(--primary-color);
+  padding: var(--spacing);
+  border-radius: var(--border-radius);
+  
+  /* With fallback */
+  color: var(--accent-color, red);
+}
+
+/* Dynamic changes */
+.dark-theme {
+  --primary-color: #0056b3;
+  --background: #222;
+  --text: #fff;
+}
+```
+
+## CSS Preprocessors
+
+### Common Features
+
+- Variables
+- Nesting
+- Mixins (reusable styles)
+- Functions
+- Imports
+
+**Popular Preprocessors**: Sass/SCSS, Less, Stylus
+
+## Best Practices
+
+### Do's
+
+- ✅ Use external stylesheets
+- ✅ Use class selectors over ID selectors
+- ✅ Keep specificity low
+- ✅ Use responsive units (rem, em, %)
+- ✅ Mobile-first approach
+- ✅ Use CSS variables for theming
+- ✅ Organize CSS logically
+- ✅ Use shorthand properties
+- ✅ Minify CSS for production
+
+### Don'ts
+
+- ❌ Use `!important` excessively
+- ❌ Use inline styles
+- ❌ Use fixed pixel widths
+- ❌ Over-nest selectors
+- ❌ Use vendor prefixes manually (use autoprefixer)
+- ❌ Forget to test cross-browser
+- ❌ Use IDs for styling
+- ❌ Ignore CSS specificity
+
+## Glossary Terms
+
+**Key Terms Covered**:
+
+- Alignment container
+- Alignment subject
+- Aspect ratio
+- Baseline
+- Block (CSS)
+- Bounding box
+- Cross Axis
+- CSS
+- CSS Object Model (CSSOM)
+- CSS pixel
+- CSS preprocessor
+- Descriptor (CSS)
+- Fallback alignment
+- Flex
+- Flex container
+- Flex item
+- Flexbox
+- Flow relative values
+- Grid
+- Grid areas
+- Grid Axis
+- Grid Cell
+- Grid Column
+- Grid container
+- Grid lines
+- Grid Row
+- Grid Tracks
+- Gutters
+- Ink overflow
+- Inset properties
+- Layout mode
+- Logical properties
+- Main axis
+- Media query
+- Physical properties
+- Pixel
+- Property (CSS)
+- Pseudo-class
+- Pseudo-element
+- Selector (CSS)
+- Stacking context
+- Style origin
+- Stylesheet
+- Vendor prefix
+
+## Additional Resources
+
+- [MDN CSS Reference](https://developer.mozilla.org/en-US/docs/Web/CSS)
+- [CSS Tricks Complete Guide to Flexbox](https://css-tricks.com/snippets/css/a-guide-to-flexbox/)
+- [CSS Tricks Complete Guide to Grid](https://css-tricks.com/snippets/css/complete-guide-grid/)
+- [Can I Use](https://caniuse.com/) - Browser compatibility tables