The comment method in CSS

Basic Syntax of CSS Comments

In CSS, /* and */ are used to wrap comment content. This commenting method is called block comments. Unlike HTML, CSS does not have a single-line comment syntax; all comments must be wrapped in these symbols.

/* This is a standard CSS comment */
body {
  font-family: Arial;
}

Comments can span multiple lines:

/*
  This is a
  multi-line CSS comment
*/
.container {
  width: 100%;
}

Common Uses of Comments

1. Code Explanation

Adding explanations to CSS rules:

/* Main navigation bar styles */
.navbar {
  background-color: #333;
  padding: 1rem;
}

/* Article content area */
.article {
  max-width: 800px;
  margin: 0 auto;
}

2. Code Grouping

Grouping related styles with comments:

/* ======================
   Layout Styles
   ====================== */
.header {
  height: 80px;
}

.main {
  display: flex;
}

/* ======================
   Component Styles
   ====================== */
.button {
  border-radius: 4px;
}

.card {
  box-shadow: 0 2px 4px rgba(0,0,0,0.1);
}

3. Temporarily Disabling Code

Comments are often used for debugging to temporarily disable certain styles:

.sidebar {
  width: 250px;
  /* display: none; */
  background-color: #f5f5f5;
}

Advanced Uses of Comments

1. Conditional Comments

Although not recommended in modern CSS, they can still be seen in specific scenarios:

/* lt IE 9 */
.old-browser {
  display: block;
}
/* end lt IE 9 */

2. Documentation Comments

Generating documentation for CSS preprocessors or tools:

/**
 * @name Primary Button
 * @description Styles for the main action button
 * @state :hover - Hover state
 * @state :active - Active state
 */
.primary-btn {
  background: blue;
}

3. Code Markers

Using special markers for easy searching:

/* TODO: Optimize responsive layout */
.responsive-grid {
  display: grid;
}

/* FIXME: Issue in Safari */
.safari-bug {
  transform: translateZ(0);
}

Comments in Preprocessors

Preprocessors like Sass/Less support two types of comments:

// This single-line comment won't appear in the compiled CSS
/* This comment will appear in the compiled output */

$primary-color: #3498db;

.button {
  // Base button styles
  padding: 10px;
  /* This comment will be retained */
  background: $primary-color;
}

Best Practices for Comments

1. Keep comments concise but informative.
2. Add explanations for complex hacks or browser-specific code.
3. Regularly clean up unused comments.
4. Use a consistent commenting style.

/* Bad comment */
/* Set color */
.color-red {
  color: red;
}

/* Good comment */
/* Special red for error message text */
.error-text {
  color: #ff0000;
}

Comments and Maintainability

Good commenting habits significantly improve code maintainability:

/* 
  Responsive breakpoint explanations:
  - sm: ≥576px (mobile landscape)
  - md: ≥768px (tablet)
  - lg: ≥992px (small desktop)
  - xl: ≥1200px (large desktop)
*/
@media (min-width: 768px) {
  .grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

Limitations of Comments

CSS comments cannot be nested. The following will cause an error:

/* Outer comment 
  /* Inner comment */
  More content */

In CSS, comment symbols (/* */) have the highest priority and will ignore all internal content, including other comment symbols.