CSS中‘*/’是什么含义？为何添加后样式效果不同？

Hey there! Great question—this is one of those tricky little syntax gotchas that can trip up even experienced developers. Let's break it down step by step.

What Does */ Mean in CSS? #

*/ is the closing marker for multi-line CSS comments. CSS uses /* to start a multi-line comment and */ to end it. The key rule here is that these markers need to come in pairs: if you start a comment with /*, you must close it with */ somewhere later in your code.

If you have a stray */ floating around without a matching opening /*, browsers will treat it as invalid syntax. Depending on where it appears, this can cause the browser to ignore the entire CSS rule (or even a chunk of code after it) because it can't parse the syntax correctly.

Why Your Two Declarations Behave Differently #

The most likely scenario is that you have an unclosed /* comment earlier in your CSS file that's affecting these lines. Let's use an example to show what's happening:

/* I forgot to close this comment!
.header {
  padding: 10px;
}

.card {
  margin-top: -17px; */ /* This */ closes the unclosed comment from above—so this margin declaration becomes active!
  border: 1px solid #ccc;
}

.footer {
  margin-top: -17px; /* This line is still inside the unclosed comment (since the first /* was only closed in the .card rule) */
}

In this case, the .card's margin-top works because the */ ends the earlier unclosed comment, pulling the declaration out of the commented section. But the .footer's margin-top is still trapped in the unclosed comment (until another */ comes along), so it never gets applied. That's why you see different styling results.

Other Special Symbols to Know in CSS #

Here are some other key syntax markers you'll encounter in CSS (and related preprocessors):

• /* ... */: Multi-line comment (must be properly paired to avoid breaking your code)
• //: Single-line comment—note: this is not standard CSS! It's supported by preprocessors like Sass/Less, and some modern browsers will parse it, but it's not officially part of CSS specs, so avoid it in plain CSS.
• @: Used for at-rules like @media (media queries), @keyframes (animations), @import (importing stylesheets), and @font-face (custom fonts).
• !important: Forces a property to take priority over other conflicting styles (use sparingly—it can make debugging harder!)
• &: A preprocessor-only symbol (Sass/Less) that represents the parent selector. For example:

  .btn {
    &:hover { background: blue; } // Compiles to .btn:hover { ... }
  }
  

• {}: Wraps the declarations inside a CSS rule set (e.g., body { background: white; })
• :: Separates a CSS property from its value (e.g., color: red;)
• ;: Ends a single CSS declaration (optional for the last declaration in a rule, but always adding it avoids syntax errors)

Quick Tip #

If you run into weird unexpected styling issues, check your comments first! Most code editors have syntax highlighting that will show unclosed comments (usually by coloring all subsequent code as part of the comment), which makes it easy to spot and fix.

内容的提问来源于stack exchange，提问作者waleedd32