6.1 Organise documents so that they may be read without style sheets.
Checkpoint
6.1 Organise documents so that they may be read without style sheets. For example, when an HTML document is rendered without associated style sheets, it must still be possible to read the document.
Organize documents so that they may be read without style sheet
It is a good practice to uses styles sheets to add appropriate presentation and layout to a website. However the structure and content of the site should still be available when style sheets are not supported – as would be the case in older web browsers - or if style sheets are turned off.
Reading Material
Web standards software and learning: complete css guide.
CSS accessibility problems: is markup dead?