CSS minification is the process of removing unnecessary characters from the CSS code, such as whitespace, comments, line breaks, and sometimes shortening property names, to reduce file size. Minifying CSS improves loading times and can have a positive impact on website performance.

1. Removing Whitespace, Line Breaks, and Comments

Minification removes unnecessary spaces, line breaks, and comments:
Before:

.container {
    margin: 20px auto;
    padding: 10px;
    background-color: #ffffff;
    border: 1px solid #dddddd;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

After Minifying:

.container{margin:20px auto;padding:10px;background-color:#fff;border:1px solid #ddd;box-shadow:0 2px 4px rgba(0,0,0,0.1);}

2. Combining Shorthand Properties

Minification tools often combine longhand properties into shorthand for further size reduction:

Before:

.box {
    margin-top: 10px;
    margin-right: 10px;
    margin-bottom: 10px;
    margin-left: 10px;
    padding: 5px 5px 5px 5px;
    border-width: 1px;
    border-style: solid;
    border-color: #333;
}

After Minifying:

.box{margin:10px;padding:5px;border:1px solid #333;}

3. Removing Units from Zero Values

CSS does not require units like px for values of 0, so minifiers remove them to save space:

Before:

.icon {
    margin: 0px;
    padding: 0px;
    border-radius: 0px;
}

After Minifying:

.icon{margin:0;padding:0;border-radius:0;}

4. Removing Duplicate Selectors

Minifying can combine duplicate selectors, which helps avoid redundancy and keeps the CSS compact:

Before:

.button {
    color: #333;
    font-size: 16px;
}

.button {
    padding: 10px;
    border-radius: 5px;
}

After Minifying:

.button{color:#333;font-size:16px;padding:10px;border-radius:5px;}

5. Shortening Colors

Hexadecimal colors can be shortened if they have repeating characters (e.g., #ffffff to #fff):

Before:

.header {
    color: #ffffff;
    background-color: #000000;
    border-color: #cccccc;
}

After Minifying:

.header{color:#fff;background-color:#000;border-color:#ccc;}

6. Merging Selectors with the Same Styles

Minifying tools will combine selectors that share the same styles:

Before:

h1 {
    font-family: Arial, sans-serif;
    font-weight: bold;
}

h2 {
    font-family: Arial, sans-serif;
    font-weight: bold;
}

After Minifying:

h1,h2{font-family:Arial,sans-serif;font-weight:bold;}

7. Using 0 Instead of none in Border Properties

When possible, using 0 instead of none can further reduce file size in minified CSS:

Before:

.card {
    border: none;
    border-radius: 0px;
}

After Minifying:

.card{border:0;border-radius:0;}

8. Removing Redundant font-family Fallbacks

Minification can remove redundant fallback fonts if they are commonly supported:

Before:

body {
    font-family: Arial, Helvetica, sans-serif;
}

After Minifying:

body{font-family:Arial,sans-serif;}

9. Combining Multiple @media Queries

CSS minifiers can also merge identical @media rules to reduce file size:

Before:

@media (max-width: 768px) {
    .header { font-size: 18px; }
}

@media (max-width: 768px) {
    .menu { display: none; }
}

After Minifying:
@media (max-width:768px){.header{font-size:18px}.menu{display:none}}

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