Have you read the Contributing Guidelines on issues?

• I have read the Contributing Guidelines on issues.

Prerequisites

• I'm using the latest version of Docusaurus.
• I have tried the npm run clear or yarn clear command.
• I have tried rm -rf node_modules yarn.lock package-lock.json and re-installing packages.
• I have tried creating a repro with https://new.docusaurus.io.
• I have read the console error message carefully (if applicable).

Description

Button style css :where selector is experimental feature and broken in many browsers. Can reproduce by visit https://docusaurus.io/ in some old version browser, the "Get Started" and "Try a Demo" button style is broken.

And I checked the css file, seems no needs to use :where selector, change them to simple css selector can fix the issue.

:where(.button--primary) {
    --ifm-button-background-color: var(--ifm-color-primary);
    --ifm-button-border-color: var(--ifm-color-primary);
}

:where(.button--primary):not(.button--outline):hover {
    --ifm-button-background-color: var(--ifm-color-primary-dark);
    --ifm-button-border-color: var(--ifm-color-primary-dark)
}

:where(.button--secondary) {
    --ifm-button-background-color: var(--ifm-color-secondary);
    --ifm-button-border-color: var(--ifm-color-secondary)
}

:where(.button--secondary):not(.button--outline):hover {
    --ifm-button-background-color: var(--ifm-color-secondary-dark);
    --ifm-button-border-color: var(--ifm-color-secondary-dark)
}

See also: https://caniuse.com/?search=where

Reproducible demo

https://docusaurus.io/

Steps to reproduce

1. Visit https://docusaurus.io/ in chrome older than version 87, or other old version browsers
2. Check the button style

Expected behavior

Expect the Button style is same as the style show in latest browser.

Actual behavior

The Button style not work, no background color.

Your environment

• Public source code: N/A
• Public site URL: https://docusaurus.io/
• Docusaurus version used: 2.0.0-beta.21
• Environment name and version: the browser in Wechat, it seems based on an old version chrome.
• Operating system and version (e.g. Ubuntu 20.04.2 LTS): Android

Self-service

• I'd be willing to fix this bug myself.