Lately, the best looking websites are more often built from a great looking theme bought from the Envato marketplace or the likes. These themes are sold for a small fee to web developers.
While so much effort goes into designing a responsive HTML5, WordPress, Magento, and more, theme, selling it for a small price of about $20 may seem pitiful. But when a $20 theme is sold 1,000 times, that becomes $20,000.
Some theme authors have multiple themes in their portfolios at any given time, with about 500 to 1,000 sales on each. The higher the quality, SEO friendly, and responsive the theme they put up for sale is, the higher their chances of selling a lot.
If you're a professional web designer, you can start designing jaw-dropping themes, and selling them online.