if()

/* Single <if-test> */
if(style(--scheme: dark): #eeeeee;)
if(media(print): black;)
if(media(width > 700px): 0 auto;)
if(supports(color: lch(7.1% 60.23 300.16)): lch(7.1% 60.23 300.16);)

/* <if-test> with else */
if(style(--size: "2xl"): 1em; else: 0.25em;)
if(media(print): white; else: black;)
if(media(width < 700px): 0 auto; else: 20px auto)
if(
  supports(color: lch(7.1% 60.23 300.16)): lch(7.1% 60.23 300.16);
  else: #03045e;
)
if(
  supports(color: lch(75% 0 0)): 3px solid lch(75% 0 0);
  else: 3px solid silver;
)

/* Multiple <if-test>s */
if(
  style(--scheme: ice): linear-gradient(#caf0f8, white, #caf0f8);
  style(--scheme: fire): linear-gradient(#ffc971, white, #ffc971);
  else: none;
)

/* <if-test> within a shorthand */
3px yellow if(
  style(--color: green): dashed;
  style(--color: yellow): inset;
  else: solid;
)

div {
  background-image: if(
    style(--scheme: ice): linear-gradient(#caf0f8, white, #caf0f8);
    style(--scheme: fire): linear-gradient(#ffc971, white, #ffc971);
    else: none;
  );
}

div {
  background-image: if(
    else: none;
    style(--scheme: ice): linear-gradient(#caf0f8, white, #caf0f8);
    style(--scheme: fire): linear-gradient(#ffc971, white, #ffc971)
  );
}

div {
  background-image: if(
    style(--scheme: ice): linear-gradient(#caf0f8, white, #caf0f8);
    else: url("debug.png");
    style(--scheme: fire): linear-gradient(#ffc971, white, #ffc971);
    else: none;
  );
}

background-color: if(else: yellow);
background-image: if();

background-image: if(
  style(--scheme: ice): linear-gradient(#caf0f8, white, #caf0f8);
  else: none;
);

background-color: if(
  style((--scheme: dark) or (--scheme: very-dark)): black;
);

background-color: if(
  style((--scheme: dark) and (--contrast: hi)): black;
);

background-color: if(
  not style(--scheme: light): black;
);

if(
  background-color: if(style(color: white): black;);
)

background-color: if(
  media(print): white;
  else: #eeeeee;
)

margin: if(
  media(width < 700px): 0 auto;
  else: 20px auto;
)

border-color: if(
  media((width > 700px) and (width < 1000px)): blue;
);

border-color: if(
  media((width < 500px) or (orientation: landscape)): blue;
);

background-color: if(
  not media(width < 500px): blue;
  else: red
);

color: if(
  supports(color: lch(75% 0 0)): lch(75% 0 0);
  else: rgb(185 185 185);
)

margin-top: if(
  supports(selector(:buffering)): 1em;
  else: initial;
)

margin-top: if(
  supports((selector(:buffering)) and (color: blue)): 1em;
);

margin-top: if(
  supports((selector(:buffering)) or (color: not-a-color)): 1em;
);

margin-top: if(
  supports(not selector(:buffering)): 1em;
);

padding: 1em;
padding: if(style(--size: "2xl"): 1em; else: 0.25em);

border: if(
  supports(color: lch(75% 0 0)): 3px solid lch(75% 0 0);
  else: 3px solid silver;
);

border: 3px solid
  if(
    supports(color: lch(75% 0 0)): lch(75% 0 0); else: silver;
  );

color: if(
  style(--scheme: ice):
    if(
      media(prefers-color-scheme: dark): #caf0f8;
      else: #03045e;
    );
  style(--scheme: fire):
    if(
      media(prefers-color-scheme: dark): #ffc971;
      else: #621708;
    );
  else: black
);

width: calc(if(
    style(--scheme: wide): 70%;
    else: 50%;
  ) - 50px);

<section style="--show-apple:true">
  <article><h2>First article</h2></article>
  <article><h2>Second article</h2></article>
</section>

html {
  height: 100%;
  font-family: sans-serif;
}

body,
section {
  height: inherit;
}

h2 {
  text-align: center;
}

article {
  background-color: cyan;
  border: 3px solid gray;
  flex: 1;
}

section {
  display: flex;
  gap: 16px;
  flex-direction: if(
    media(orientation: landscape): row;
    else: column;
  )
}

h2::before {
  content: if(
    style(--show-apple: true): "🍎 ";
  );
}

h2 {
  color: if(
    supports(color: lch(29.57% 43.25 344.44)): lch(29.57% 43.25 344.44);
    else: #792359;
  )
}

<article>
  <h1>Main heading</h1>
  <p>
    Lorem ipsum dolor sit amet consectetur adipiscing elit.
    Quisque faucibus ex sapien vitae pellentesque sem placerat.
    In id cursus mi pretium tellus duis convallis.
  </p>
  <aside>
    <h2>An aside</h2>
    <p>
      Tempus leo eu aenean sed diam urna tempor. Pulvinar vivamus
      fringilla lacus nec metus bibendum egestas.
    </p>
  </aside>
  <p>
    Iaculis massa nisl malesuada lacinia integer nunc posuere. Ut
    hendrerit semper vel class aptent taciti sociosqu. Ad litora
    torquent per conubia nostra inceptos himenaeos.
  </p>
</article>
<form>
  <label for="scheme">Choose color scheme:</label>
  <select id="scheme">
    <option value="">Default</option>
    <option value="ice">Ice</option>
    <option value="fire">Fire</option>
  </select>
</form>

const articleElem = document.querySelector("article");
const selectElem = document.querySelector("select");

selectElem.addEventListener("change", () => {
  articleElem.className = selectElem.value;
});

* {
  box-sizing: border-box;
}

html {
  font-family: "Helvetica", "Arial", sans-serif;
}

p {
  line-height: 1.5;
}

form {
  padding-left: 20px;
  margin-top: 20px;
}

article h2 {
  margin: 0;
  font-size: 1.8rem;
}

body {
  max-width: 700px;
  margin: if(
    media(width < 700px): 0;
    else: 20px;
  ) auto 0;
}

.ice {
  --scheme: ice;
}

.fire {
  --scheme: fire;
}

article {
  padding: 20px;
  --color1: if(
    style(--scheme: ice): #03045e;
    style(--scheme: fire): #621708;
    else: black;
  );
  --color2: if(
    style(--scheme: ice): #caf0f8;
    style(--scheme: fire): #ffc971;
    else: white;
  );

  color: var(--color1);
  border: 3px solid var(--color1);
  background-image: linear-gradient(
    to left,
    var(--color2),
    white,
    var(--color2)
  );
}

aside {
  color: var(--color2);
  background-color: var(--color1);
  padding: 20px;
}

h1 {
  margin: 0;
  font-size: if(
    media(width > 700px): calc(3rem + 2vw);
    else: 3rem;
  );
}

h1::before {
  content: if(
    style(--scheme: ice): "❄️ ";
    style(--scheme: fire): "🔥 ";
    else: "";
  );
}