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              <header>
  Native CSS Variables Introduce DEMO III<br />
  <a href="http://muki.tw/tech/native-css-variables" target="_blank">(http://muki.tw/tech/native-css-variables)</a>
</header>

<section>
  <p>利用 JS 讀取我的背景顏色為<span id="color-name"></span></p>
  <p id="change">利用 JS 將背景顏色改為藍色</p>
</section>
            
          
!
            
              @import "compass/css3";

/**
Native CSS Variables Introduce DEMO III
Autohr: Muki Wu
Article: http://muki.tw/tech/native-css-variables
**/

/* basic layout start (you can skip it) */
body {
  background: #333;
  font-size: 16px;
  color: #f0f0f0;
  line-height: 1.1em;
}
a {
  text-decoration: none;
  color: #313131;
  &:hover {
    color: #000;
  }
}
section {
  width: 500px;
  margin: 0 auto;
  background: #555;
  padding: 1em;
  div {
    margin: 0 0 2em 0;
  }
}
header {
  background: #d9444a;
  text-align: center;
  color: #fff;
  padding: .7em 0;
  a {
    color: rgba(255,255,255,.6);
    @include text-shadow(1px 1px 1px #973735);
  }
  &:after {
    content: " ";
    position: absolute;
    width: 0;
    height: 0;
    border-width: 10px;
    border-style: solid;
    border-color: #d9444a transparent transparent transparent;
    top: 53px;
    left: 50%;
  }
}

h2 {
  font-size: 1em;
  margin: 0 0 .5em 0;
  background: #444;
  display: inline-block;
  padding: .5em 1.2em;
  position: relative;
  left: -1em;
}

/* demo code start */

:root {
  --bg-primary-color: #d9444a;
}

p {
  background: var(--bg-primary-color);
}
            
          
!
            
              var styles = getComputedStyle(document.documentElement);
var value = String(styles.getPropertyValue('--bg-primary-color')).trim();

/* 讀取背景顏色 */
document.getElementById("color-name").innerHTML=value;

/* 修改背景顏色 */
// document.documentElement.style.setProperty('--bg-primary-color', '#369');
            
          
!
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