css变量的常见应用

声明变量

html {
  --brand-color: hsl(230, 80%, 60%);
}

.logo {
  fill: pink; /* fallback */
  fill: var(--brand-color);
}

<svg version="1.1" viewBox="0 0 50 50" class="logo">   
  
  <circle cx="25" cy="25" r="25" />
svg>

设置默认值

.button {
  /* --roundness: 2px; */
  border-radius: var(--roundness, 10px);
}

定制化&覆盖

.message {
  background-color: var(--student-background, #fff);
  color: var(--student-color, #000);
  font-family: var(--student-font, "Times New Roman", serif);
  margin-bottom: 10px;
  padding: 10px;
}

[data-student-theme="rachel"] {
  --student-background: rgb(43, 25, 61);
  --student-color: rgb(252, 249, 249);
  --student-font: Arial, sans-serif;
}

[data-student-theme="jen"] {
  --student-background: #d55349;
  --student-color: #000;
  --student-font: Avenir, Helvetica, sans-serif;
}

[data-student-theme="tyler"] {
  --student-background: blue;
  --student-color: yellow;
  --student-font: "Comic Sans MS", "Comic Sans", cursive;
}

<section>
  <div data-student-theme="chris">
    <p class="message">Chris: I've spoken at events and given workshops all over the world at conferences.p>
  div>
  <div data-student-theme="rachel">
    <p class="message">Rachel: I prefer email over other forms of communication.p>
  div>
  <div data-student-theme="jen">
    <p class="message">Jen: This is why I immediately set up my new team with Slack for real-time chat.p>
  div>
  <div data-student-theme="tyler">
    <p class="message">Tyler: I miss AIM and MySpace, but this message board is okay.p>
  div>
section>

.readable-theme [data-student-theme] {
  --student-background: hsl(50, 50%, 90%);
  --student-color: hsl(200, 50%, 10%);
  --student-font: Verdana, Geneva, sans-serif;
}

<section class="readable-theme">
  ...
section>

规则集

a {
  --link: hsl(230, 60%, 50%);
  --link-visited: hsl(290, 60%, 50%);
  --link-hover: hsl(230, 80%, 60%);
  --link-active: hsl(350, 60%, 50%);
}

a:link {
  color: var(--link);
}

a:visited {
  color: var(--link-visited);
}

a:hover {
  color: var(--link-hover);
}

a:active {
  color: var(--link-active);
}

.grayscale {
  --link: LightSlateGrey;
  --link-visited: Silver;
  --link-hover: DimGray;
  --link-active: LightSteelBlue;
}

<a href="#" class="grayscale">Link Examplea>  

eg.定制化

.custom-link {
  --hue: 30;
  --link: hsl(var(--hue), 60%, 50%);
  --link-visited: hsl(calc(var(--hue) + 60), 60%, 50%);
  --link-hover: hsl(var(--hue), 80%, 60%);
  --link-active: hsl(calc(var(--hue) + 120), 60%, 50%);
}

.danger {
  --hue: 350;
}

<a href="#" class="custom-link">Link Examplea>
<a href="#" class="custom-link danger">Link Examplea>

行内使用自定义属性

.grid {
  --columns: auto-fit;

  display: grid;
  gap: 10px;
  grid-template-columns: repeat(var(--columns), minmax(0, 1fr));
}

<div class="grid">
  <img src="https://www.fillmurray.com/900/600" alt="Bill Murray" />
  <img src="https://www.placecage.com/900/600" alt="Nic Cage" />
  <img src="https://www.placecage.com/g/900/600" alt="Nic Cage gray" />
  <img src="https://www.fillmurray.com/g/900/600" alt="Bill Murray gray" />
  <img src="https://www.placecage.com/c/900/600" alt="Nic Cage crazy" />
  <img src="https://www.placecage.com/gif/900/600" alt="Nic Cage gif" />
div>

<div class="grid" style="--columns: 3;">
  ...
div>