全屏 | :fullscreen

/* Selects any <div> as long as it is being displayed in fullscreen mode */
/* Implemented in Gecko, Edge/IE, and WebKit/Chrome using prefixes */
/* Edge also supports the non-prefixed version */
div:-webkit-full-screen {
  background-color: pink;
}

div:-moz-full-screen {
  background-color: pink;
}

div:-ms-fullscreen {
  background-color: pink;
}

div:fullscreen {
  background-color: pink;
}

:fullscreen

<div id="fullscreen">
  <h1>:fullscreen Demo</h1>
  <p> This will become big red text when the browser is in fullscreen mode.</p>
  <button id="fullscreen-button">Enter Fullscreen</button>
</div>

#fullscreen:fullscreen {
  padding: 42px;
  background-color: pink;
  border:2px solid #f00;
  font-size: 200%;
}

#fullscreen:fullscreen > h1 {
  color: red;
}

#fullscreen:fullscreen > p {
  color: DarkRed;
}

#fullscreen:fullscreen > button {
  display: none;
}