For a font size of 16px, the perfect line height is achieved when h equals the golden ratio. This yields a value of 25.88854px for the optimal line height. Using this value, you can then determine that the associated optimal line width is 670.21670px.
CSS Lint points out problems with your CSS code. It does basic syntax checking as well as applying a set of rules to the code that look for problematic patterns or signs of inefficiency. The [rules] are all pluggable, so you can easily write your own or omit ones you don't want.
CodePen is an HTML, CSS, and JavaScript code editor right in your browser with instant previews of the code you see and write. It's great for showing off your work and seeing what amazing things other people are doing with the web. It's also great for troubleshooting problems and getting critique.