Using Firefox, go to the View->Zoom menu and activate ‘Zoom Text Only’. This will allow you to manually increase the text size on the page (hold down the Ctrl key and scroll the middle mouse button).
Make sure your browser is wide enough so that the ‘Latest Courses’ feature is displayed as a column to the right of ‘The Best Way to learn About Web development’ header. Now go ahead and manually increase the text size. You’ll notice that at some point the ‘Latest Courses’ feature drifts off the right side of the page and there is a horizontal scroll bar. While your page is responsive to changes in the in the view port width it is not responsive to changes in text size.
The fix for this is rather easy. Change your CSS break points from px values to em values. Just divide the px value by 16 to get the em value.