Making something bold makes it more important for search engine ranking and even improves readability for humans.To get the search engine ranking benefit, do we need to use <b> or <strong> tag or are CCS rules to do this recognized?In other words, do search engine crawlers actually read and apply CSS when analyzing content?
Do Search Engines Crawlers Read CSS?
seo;css
The generally accepted way to emphasise text is to use the <strong> tag. You can then style that using CSS.Looking through our logs I can see some evidence that some spiders fetch CSS files. Specifically,Googlebot-Image/1.0DoCoMo/2.0 (compatible; Googlebot-Mobile/2.1)Googlebot (http://www.google.com/bot.html)Anecdotally there's evidence that some search engines use this to detect if text is being hidden (and therefore someone is trying to fool a search engine with bogus keywords).I think your safest bet is to use <strong> and don't rely purely on CSS to emphasise important words or phrases.