On Friday, we told you that it was safe to have more than 100 links on a single web page when using them within your primary navigation. You could also hide several links within CSS dropdown menus.
The use of advanced CSS techniques in your website design allow for features that are very nicely user interactive.
Hiding text on a web page is an old black hat SEO technique. Some people would disguise keyword rich text in black color on a black background. You could also use white text on a white background. The effect is that the text is invisible to users but not to Google.
Another technique used by black hat SEOs is the hiding of a lot of text inside an invisible area that users can't see, but Google can.
The intent of these hidden text methods is to influence organic ranking.
However, with CSS, we can hide blocks of text until the user clicks a "read more" button, or maybe a "next step" button. Some product catalogs will use this technique to show product details when you hover over a thumbnail.
Using this CSS hidden text technique should not be feared, as long as you do it correctly. Google will not penalize you if you only have a few sentences of text inside those hidden areas. They don't exactly tell us how many words to limit to but our recommendation is to keep it less than 250 words.
We don't recommend having large blocks of hidden text on a single page. A good rule of thumb is to measure if you have more information being hidden by default or visible by default. If more of your text is hidden then you may find yourself dropping in website ranking.
We've also noticed something about e-commerce product catalogs that we need to warn you of. As we said above, a common technique is to have product information appear when someone hovers over a product thumbnail. This is a handy feature to give the user a reason to click for more details. However, you should not use this feature to provide the full details of the item.
Most likely, if you provide full details of every item, you will have more hidden content on your web page by default that visible. So just limit this type of product information to just enough to satisfy the user, while making them want to click to find out more.
New techniques of CSS are great for website design, but also cause interesting new SEO issues. You might have to test new design ideas and roll them back if they work against you.