WCAG 2.1 - SC 1.3.1 Info and Relationships

Make sure that information about the meaning and structure of your content are conveyed by more than the visual presentation of your content.

Official Requirements:

1.3.1 Info and Relationships: Information, structure, and relationships conveyed through presentation can be programmatically determined or are available in text.

How to fix:

• Use HTML's semantic elements to convey meaning, rather than visual presentation. For example, use an H3 element, rather than bolded and colored text set off by a line break. Use real list markup rather than a table of text and bullet images. Use paragraphs rather than a couple of line breaks. HTML 5 contains many new useful semantic elements.
• Use label elements to associate form labels with their elements.
• Use color and text to indicate required fields.
• Use the TH element, with the scope attribute, to indicate table structure.