… for text and background. The more visible the text, the faster users are able to scan and read it. The W3C recommends the following contrast ratios for body text and image text:
…te space between lines of text, generally improving readability in exchange for screen real estate. As a rule, leading should be about 30% more than the character height for good readability.
In web design you can achieve an optimal number of characters per line by restricting the width of your text blocks using em or pixels.