In W3.CSS, the basic grid system is based on a 12-column layout.

This means that the grid is divided into 12 equal-width columns, and you can use different combinations of these columns to structure your layout. Each element can span across one or more of these columns, depending on the desired width for that element.

Key Points about the W3.CSS Grid:

1. 12 Columns: The default grid system is based on 12 columns. You can divide the screen into 12 equal parts, with each column taking up one fraction (1/12) of the screen width.
2. Responsive Layout: W3.CSS provides responsive features, meaning the grid can adapt to different screen sizes, such as mobile, tablet, and desktop views.
3. Column Sizing: You can control how many columns an element should span using class names like w3-col and modifiers such as w3-col s4, w3-col m6, or w3-col l3, where the number indicates how many columns it should span out of the total 12 columns.

Example:

In this example:

• On small screens (s12), each column takes up the full width.
• On medium screens (m6), each column spans 6 columns (half of the grid).
• On large screens (l4), each column spans 4 columns (a third of the grid).