initial

Baseline Widely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since November 2015.

CSS 关键字 initial 将属性的初始（或默认）值应用于元素。不应将初始值与浏览器样式表指定的值混淆。它可以应用于任何 CSS 属性。这包括 CSS 简写 all，initial 可用于将所有 CSS 属性恢复到其初始状态。

备注： 在继承的属性上，初始值可能是意外的。你应该考虑使用 inherit, unset，或revert 关键字代替。

html

<p>
  <span>This text is red.</span>
  <em>This text is in the initial color (typically black).</em>
  <span>This is red again.</span>
</p>

css

p {
  color: red;
}

em {
  color: initial;
}

Specification
CSS Cascading and Inheritance Level 4 # initial

BCD tables only load in the browser

Use unset to set a property to its inherited value if it inherits, or to its initial value if not.
Use revert to reset a property to the value established by the user-agent stylesheet (or by user styles, if any exist).
Use inherit to make an element's property the same as its parent.
The all property lets you reset all properties to their initial, inherited, reverted, or unset state at once.