W3.CSS Starter Example

This is a w3-container

The w3-container class just adds 16px left and right padding to any block. You could add the w3-padding class to add some top and bottom padding.

This is a w3-container

This uses my style class (not part of framework) for centered content.
This again uses my style class (not part of framework) for centered content.
It's responsive because of (max-width: 1100px;) (try it by resizing your browser!)
If it instead had (width: 1100px;), it would be fixed-width (not responsive).

Below is a w3-row of columns

The w3-row class does nothing other than clear the float to serve as a convenient wrapper for columns (w3-col).
Observe how the columns behave across the @media query breakpoints and see why in the HTML where the column behavior is set.
cat
bat
rat

Below is a w3-row of columns

These columns are inside my centered content wrapper. Observe the column behavior on different device widths and see why in the HTML.
cat
bat
rat
gnat