CSS 3 cheatsheet

<link href="./path/to/stylesheet/style.css" rel="stylesheet" type="text/css" />

<style>
  body {
    background-color: linen;
  }
</style>

<h2 style="text-align: center;">Centered text</h2>

<p style="color: blue; font-size: 18px;">Blue, 18-point text</p>

<div class="classname"></div>
<div class="class1 classn ..."></div>

.post-title {
  color: blue !important;
}

h1 {
}
#job-title {
}
div.hero {
}
div > p {
}

color: #2a2aff;
color: green;
color: rgb(34, 12, 64, 0.6);
color: hsla(30 100% 50% / 0.6);

background-color: blue;
background-image: url('nyan-cat.gif');
background-image: url('../image.png');

.page-title {
  font-weight: bold;
  font-size: 30px;
  font-family: 'Courier New';
}

.box {
  position: relative;
  top: 20px;
  left: 20px;
}

animation: 300ms linear 0s infinite;

animation: bounce 300ms linear infinite;

/* This is a single line comment */

/* This is a 
   multi-line comment */

div {
  display: flex;
  justify-content: center;
}
div {
  display: flex;
  justify-content: flex-start;
}

#container {
  display: grid;
  grid: repeat(2, 60px) / auto-flow 80px;
}

#container > div {
  background-color: #8ca0ff;
  width: 50px;
  height: 50px;
}

counter-set: subsection;
counter-increment: subsection;
counter-reset: subsection 0;

:root {
  --bg-color: brown;
}
element {
  background-color: var(--bg-color);
}

font-family: Arial, sans-serif;
font-size: 12pt;
letter-spacing: 0.02em;

@font-face {
  font-family: 'Glegoo';
  src: url('../Glegoo.woff');
}

color: red;
color: orange;
color: tan;
color: rebeccapurple;

color: #090;
color: #009900;
color: #090a;
color: #009900aa;

color: rgb(34, 12, 64, 0.6);
color: rgba(34, 12, 64, 0.6);
color: rgb(34 12 64 / 0.6);
color: rgba(34 12 64 / 0.3);
color: rgb(34 12 64 / 60%);
color: rgba(34.6 12 64 / 30%);

color: hsl(30, 100%, 50%, 0.6);
color: hsla(30, 100%, 50%, 0.6);
color: hsl(30 100% 50% / 0.6);
color: hsla(30 100% 50% / 0.6);
color: hsl(30 100% 50% / 60%);
color: hsla(30.2 100% 50% / 60%);

color: inherit;
color: initial;
color: unset;
color: transparent;

color: currentcolor; /* keyword */

background: url(img_man.jpg) no-repeat center;

background:
  url(img_flwr.gif) right bottom no-repeat,
  url(paper.gif) left top repeat;

background: rgb(2, 0, 36);
background: linear-gradient(
  90deg,
  rgba(2, 0, 36, 1) 0%,
  rgba(13, 232, 230, 1) 35%,
  rgba(0, 212, 255, 1) 100%
);

.column {
  max-width: 200px;
  width: 500px;
}

.block-one {
  margin: 20px;
  padding: 10px;
}

.container {
  box-sizing: border-box;
}

.invisible-elements {
  visibility: hidden;
}

div {
  margin: auto;
}

.small-block {
  overflow: scroll;
}

/* @keyframes duration | timing-function | delay |
   iteration-count | direction | fill-mode | play-state | name */
animation: 3s ease-in 1s 2 reverse both paused slidein;

/* @keyframes duration | timing-function | delay | name */
animation: 3s linear 1s slidein;

/* @keyframes duration | name */
animation: 3s slidein;

animation: 4s linear 0s infinite alternate move_eye;
animation: bounce 300ms linear 0s infinite normal;
animation: bounce 300ms linear infinite;
animation: bounce 300ms linear infinite alternate-reverse;
animation: bounce 300ms linear 2s infinite alternate-reverse forwards normal;

.one('webkitAnimationEnd oanimationend msAnimationEnd animationend')

.container {
  display: flex;
}

.container > div {
  flex: 1 1 auto;
}

/* This: */
flex: 1 0 auto;

/* Is equivalent to this: */
flex-grow: 1;
flex-shrink: 0;
flex-basis: auto;

order: 1;

align-self: flex-start; /* left */
margin-left: auto; /* right */

.container {
  display: flex;
}

.container > div {
  width: 100px;
  height: 100px;
  margin: auto;
}

.container {
  display: flex;

  /* vertical */
  align-items: center;

  /* horizontal */
  justify-content: center;
}

.container > .top {
  order: 1;
}

.container > .bottom {
  order: 2;
}

.container {
  display: flex;
  flex-direction: column;
}

.container > .top {
  flex: 0 0 100px;
}

.container > .content {
  flex: 1 0 auto;
}

.container {
  display: flex;
}

/* the 'px' values here are just suggested percentages */
.container > .checkbox {
  flex: 1 0 20px;
}
.container > .subject {
  flex: 1 0 400px;
}
.container > .date {
  flex: 1 0 120px;
}

.container {
  align-items: center;
}

.menu > .left {
  align-self: flex-start;
}
.menu > .right {
  align-self: flex-end;
}

#grid-container {
  display: grid;
  width: 100px;
  grid-template-columns: 20px 20% 60%;
}

.grid {
  display: grid;
  width: 100px;
  grid-template-columns: 1fr 60px 1fr;
}

/*The distance between rows is 20px*/
/*The distance between columns is 10px*/
#grid-container {
  display: grid;
  grid-gap: 20px 10px;
}

#grid-container {
  display: block;
}

.item {
  grid-row: 1 / span 2;
}

#grid-container {
  display: inline-grid;
}

.grid {
  display: grid;
  grid-template-columns: 100px minmax(100px, 500px) 100px;
}

grid-row-start: 2;
grid-row-end: span 2;

grid-row-gap: length;

.item1 {
  grid-area: 2 / 1 / span 2 / span 3;
}

#container {
  display: grid;
  justify-items: center;
  grid-template-columns: 1fr;
  grid-template-rows: 1fr 1fr 1fr;
  grid-gap: 10px;
}

.item {
  grid-area: nav;
}
.grid-container {
  display: grid;
  grid-template-areas:
    'nav nav . .'
    'nav nav . .';
}

#grid-container {
  display: grid;
  justify-items: start;
}

.grid-items {
  justify-self: end;
}

#container {
  display: grid;
  align-items: start;
  grid-template-columns: 1fr;
  grid-template-rows: 1fr 1fr 1fr;
  grid-gap: 10px;
}

:root {
  --first-color: #16f;
  --second-color: #ff7;
}

#firstParagraph {
  background-color: var(--first-color);
  color: var(--second-color);
}

/* Set "my-counter" to 0 */
counter-set: my-counter;

/* Increment "my-counter" by 1 */
counter-increment: my-counter;

/* Decrement "my-counter" by 1 */
counter-increment: my-counter -1;

/* Reset "my-counter" to 0 */
counter-reset: my-counter;

body {
  counter-reset: section;
}

h3::before {
  counter-increment: section;
  content: 'Section.' counter(section);
}

ol {
  counter-reset: section;
  list-marker-type: none;
}

li::before {
  counter-increment: section;
  content: counters(section, '.') ' ';
}

html {
  scroll-behavior: smooth;
}

.element-wrap {
  container: element / inline-size;
}
@container element (min-inline-size: 300px) {
  .element {
    display: flex;
    gap: 1rem;
  }
}

.container {
  --variant: 1;

  &.variant2 {
    --variant: 2;
  }
}

@container style(--variant: 1) {
  button {
  } /* You can't style .container, but can select inside it */
  .other-things {
  }
}

@container style(--variant: 2) {
  button {
  }
  .whatever {
  }
}

.card {
  padding: 5cqi;
  font-size: 4cqi;
  border: 1cqi solid brown;
  height: 100%;
}

h2 {
  font-size: 10cqi;
  margin-block: 0 3cqi;
}

figure:has(figcaption) {
  border: 1px solid black;
  padding: 0.5rem;
}

.cards {
  .card {
    & .card-description {
      color: blue;
    }
    & .card-title {
      color: red;
    }
  }
}

@scope {
  :scope {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 1rem;
    padding: 1rem;
    border: 1px solid black;
  }
  .card {
    padding: 1rem;
    border: 1px solid black;
    background: lightgray;
    h2 {
      margin: 0 0 1rem 0;
    }
  }
}

/* Specify the order to apply styles in cascade */
@layer legacyCard, newCard;

/* Imagine you have a lot of styles */
@layer newCard {
  .card {
    background-color: red;
  }
}
@layer legacyCard {
  .card {
    background-color: green;
  }
}

button {
  background-color: #4caf50;
  border: none;
  color: white;
  padding: 0.5rem 1.5rem;
  text-decoration: none;
  font: inherit;
  border-radius: 4px;
  .icon {
    position: relative;
    top: 0.125em;
    fill: white;
    width: 1em;
    aspect-ratio: 1;
    margin-inline-end: 0.25rem;
  }
}

<div class="container">
  <div class="swatch">
    <style contenteditable>
      @scope {
        :scope {
          background-color: color(display-p3 1 0.5 0);
        }
      }
    </style>
  </div>
  <div class="swatch">
    <style contenteditable>
      @scope {
        :scope {
          background-color: oklch(61.88% 0.286 342.4);
        }
      }
    </style>
  </div>
  <div class="swatch">
    <style contenteditable>
      @scope {
        :scope {
          background-color: oklab(0.73 0.15 0.16);
        }
      }
    </style>
  </div>

  <div class="swatch">
    <style contenteditable>
      @scope {
        :scope {
          background-image: linear-gradient(to right in oklch, red, blue);
        }
      }
    </style>
  </div>

  <div class="swatch">
    <style contenteditable>
      @scope {
        :scope {
          background-image: linear-gradient(to right in oklab, red, blue);
        }
      }
    </style>
  </div>

  <div class="swatch">
    <style contenteditable>
      @scope {
        :scope {
          background-image: linear-gradient(to right in srgb, red, blue);
        }
      }
    </style>
  </div>
</div>

.swatch {
  color: white;
  width: 100px;
  aspect-ratio: 1;
  display: grid;
  place-items: center;
  text-align: center;

  &:nth-child(1) {
    background-color: var(--bg);
  }
  &:nth-child(2) {
    background-color: color-mix(in oklch, var(--bg), black 30%);
  }
  &:nth-child(3) {
    background-color: color-mix(in oklch, var(--bg), white 30%);
  }
}

.container {
  /* prevent "extra" margin at the end of the element */
  margin-trim: block-end;

  /* an element like this might be the culprit, but it could be anything */
  > p {
    margin-block-end: 1rem;
  }
}

.balance {
  text-wrap: balance;
}
.pretty {
  text-wrap: pretty;
}

html {
  font-family: system-ui, sans-serif;
}

main {
  max-inline-size: 60ch;
  margin-inline: auto;
}

.grid {
  display: grid;
  grid-template-columns: repeat(9, 1fr);
  grid-template-rows: repeat(4, minmax(100px, auto));
}

.item {
  display: grid;
  grid-column: 2 / 7;
  grid-row: 2 / 4;
  grid-template-columns: subgrid;
  grid-template-rows: repeat(3, 80px);
}

.subitem {
  grid-column: 3 / 6;
  grid-row: 1 / 3;
}