kebab-case

Example: main-container, btn-primary

Why?

• Suitable for CSS and HTML, as classes and IDs cannot contain spaces.
• Highly readable within files.
• Also used for file names.

Practical example

<div class="main-container"></div>

.main-container {
  padding: 20px;
}

Advantages: readable, web-friendly. Disadvantage: cannot be used in JS (the - is interpreted as a subtraction operator).