MacOS – Specify Minimum Font Size in Safari 10.0, macOS Sierra

Your question doesn't provide a lot of detail, and it's also a little ambiguous (hence the comments you're getting).

Here is an answer assuming you're wanting to do this for your own personal web browsing, rather than as a web developer. This answer also assumes you're trying to only reduce the font size rather than the whole page.

Since there's no way to do this through Safari's preferences, you have two options open to you:

1. Using a custom style sheet
2. Installing an extension

Style sheet

If you know how to create your own style sheet, then follow these steps:

1. Create a style sheet to set your font properties
2. Go to the Safari > Preferences menu
3. Select the Advanced tab
4. In the Style Sheet drop-down menu, select Other...
5. Navigate to your style sheet and select it
6. Exit the Safari preferences.

Extension

There are probably many extensions that will achieve what you want. Here are the steps for one that I'm aware of:

1. Go to: https://safari-extensions.apple.com/details/?id=com.sobolev.stylish-5555L95H45
2. Install the Stylish extension
3. Restart Safari
4. Take note that to the left of the address bar you should now see the Stylish S button
5. Go to: https://userstyles.org/styles/68263/global-font-size
6. Click on the Install with Stylish button
7. You've now installed this style

Now, if you need to customise this style, do the following:

1. click on the Stylish S button I referred to at Step 4 above.
2. Click on Manage
3. Under the Global Font Size option click on Edit
4. This displays the CSS code for this style. Edit it as you need.
5. Save your changes

Hope this helps.

If I've misunderstood your question, please clarify it.

Seems like this an issue with digicert's OCSP and Роскомнадзор. macOS tries to check certificate revocation every time when you change Safari tab with digicert certificate, but IP address is blocked by provider. Same issue with App Store downloads.

I've added different IP address to the /etc/hosts:

72.21.91.29 ocsp.digicert.com

and everything works fine for me now.

Also you can try other solutions or check details from https://stackoverflow.com/questions/39899002/github-is-painfully-slow-on-safari-macos-sierra-10-12