Readable text is a paramount factor in website user retention

Assuming your just designing, not developing, readability is the most important feature of a website. If visitors cannot read the text on your website because the font is too small or there isn't enough contrast, they will leave.

Font Size

For readability, use at least 16 pixels for your body text. Most people believe 12 pixels is fine for body text, but browsers default to 16 pixels for a reason. People can zoom in on your text, but hitting the back button is easier.

Font Type

Use easy-to-read sans-serif fonts. Fun fonts are okay headers and your logo. If you decide to use a fancy font in the body text, as opposed to an easy-to-read font, you'll give your visitors a headache.

Contrast

For readability, black text on a white background is best, which is why a majority of websites use this combination. Black on white isn't a good choice for everyone; if you want a dark background, use a light text, but not a bright white, as this combination causes eye fatigue. Stay away from using a bright color for a background with contrasting bright text as well.

Backgrounds

With a white content background, you can select a brighter body background, or one with static images. You can still do the same if your content background is a complimentary color with a highly readable font color, although, this works best with gaming sites. You never want a background that is too distracting for your readers.

If you're a web designer, you'll eventually have a client that wants a smaller font or a fancy font that they found online that will make their site stand out. It's up to you to tell your clients the reasons that their ideas will not work. You can do what your client wants; you can make their website with 10 pixel text in the body if they insist, but you may not want to include the website in your portfolio. For more information click here https://imgur.com/a/UeaOO.