Class Selector

The class selector matches elements by their class attribute value. It is denoted by a period (.) followed by the class name and has a specificity of 2-4 points depending on the number of classes.

Usage

.classname {
    property: value;
}

Class selectors can match multiple elements that share the same class and can be combined for more specific targeting.

Syntax Examples

/* Single class */
.highlight {
    background-color: yellow;
}

/* Multiple classes (both must be present) */
.important.urgent {
    color: red;
    font-weight: bold;
}

/* Class with element type */
p.intro {
    font-size: 14pt;
}

Specificity

Single class: 2 points
Double class: 3 points
Triple class: 4 points

Notes

Class names are case-sensitive
An element can have multiple classes (space-separated in HTML)
The selector .class1.class2 matches elements that have both class1 AND class2
Class selectors are reusable across multiple elements
More specific than element selectors but less specific than ID selectors

Examples

Example 1: Basic class styling

<style>
    .highlight {
        background-color: yellow;
        padding: 5pt;
    }
</style>
<body>
    <p class="highlight">This paragraph is highlighted.</p>
    <p>This paragraph is not.</p>
    <span class="highlight">This span is also highlighted.</span>
</body>

Example 2: Multiple classes on one element

<style>
    .large {
        font-size: 16pt;
    }

    .bold {
        font-weight: bold;
    }

    .red {
        color: red;
    }
</style>
<body>
    <p class="large bold">Large and bold text.</p>
    <p class="large red">Large and red text.</p>
    <p class="bold red">Bold and red text.</p>
</body>

Example 3: Multi-class selector

<style>
    .warning.important {
        color: red;
        font-weight: bold;
        border: 2pt solid red;
        padding: 10pt;
    }
</style>
<body>
    <div class="warning">This is just a warning.</div>
    <div class="important">This is just important.</div>
    <div class="warning important">This is both - styled with red border!</div>
</body>

Example 4: Element with class

<style>
    p.intro {
        font-size: 14pt;
        font-weight: bold;
        color: #333;
    }

    div.intro {
        background-color: #f0f0f0;
        padding: 20pt;
    }
</style>
<body>
    <p class="intro">Intro paragraph with special styling.</p>
    <div class="intro">Intro div with different styling.</div>
</body>

Example 5: Card layout pattern

<style>
    .card {
        border: 1pt solid #ddd;
        border-radius: 4pt;
        padding: 15pt;
        margin-bottom: 10pt;
    }

    .card-header {
        font-size: 16pt;
        font-weight: bold;
        margin-bottom: 10pt;
    }

    .card-body {
        font-size: 12pt;
        line-height: 1.5;
    }
</style>
<body>
    <div class="card">
        <div class="card-header">Card Title</div>
        <div class="card-body">Card content goes here.</div>
    </div>
</body>

Example 6: Alert boxes

<style>
    .alert {
        padding: 12pt;
        margin-bottom: 10pt;
        border: 1pt solid transparent;
    }

    .alert-success {
        color: #155724;
        background-color: #d4edda;
        border-color: #c3e6cb;
    }

    .alert-danger {
        color: #721c24;
        background-color: #f8d7da;
        border-color: #f5c6cb;
    }
</style>
<body>
    <div class="alert alert-success">Operation successful!</div>
    <div class="alert alert-danger">Error occurred!</div>
</body>

Example 7: Text utility classes

<style>
    .text-center {
        text-align: center;
    }

    .text-right {
        text-align: right;
    }

    .text-muted {
        color: #6c757d;
    }

    .text-uppercase {
        text-transform: uppercase;
    }
</style>
<body>
    <p class="text-center">Centered text</p>
    <p class="text-right text-muted">Right-aligned muted text</p>
    <p class="text-uppercase">uppercase text</p>
</body>

Example 8: Spacing utilities

<style>
    .m-0 { margin: 0; }
    .m-1 { margin: 5pt; }
    .m-2 { margin: 10pt; }

    .p-0 { padding: 0; }
    .p-1 { padding: 5pt; }
    .p-2 { padding: 10pt; }
</style>
<body>
    <div class="m-2 p-2">Box with margin and padding</div>
    <div class="m-0 p-1">Different spacing</div>
</body>

Example 9: Table row styling

<style>
    .table-row-even {
        background-color: #f2f2f2;
    }

    .table-row-highlight {
        background-color: #ffffcc;
        font-weight: bold;
    }
</style>
<body>
    <table>
        <tr><td>Row 1</td></tr>
        <tr class="table-row-even"><td>Row 2</td></tr>
        <tr><td>Row 3</td></tr>
        <tr class="table-row-even table-row-highlight"><td>Row 4</td></tr>
    </table>
</body>

Example 10: Combined with data binding

<style>
    .product-name {
        font-size: 14pt;
        font-weight: bold;
    }

    .product-price {
        color: #28a745;
        font-size: 16pt;
    }
</style>
<body>
    <div data-bind="">
        <div class="product-name"></div>
        <div class="product-price">$</div>
    </div>
</body>