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CSS

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HTML 

              
                <div class="content-container">
  <header>
    <h1>Defensive CSS</h1>
    <h2>Flex Wrapping</h2>
  </header>
  <main>
    <p>Since CSS flexbox gained wide support, its most frequent issue concerns items overflowing their container. This is because, by default, flex items do not wrap to a new row when they reach the edge of their container. To prevent this, and ensure flex items wrap to new lines as needed, always include a <code class="inline">flex-wrap</code> property on every flex container.</p>

    <div class="content-section">
      <section class="demo">
        <h3>Without Defensive CSS</h3>
        <div class="flex-container">
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
        </div>
      </section>

      <section class="demo">
        <h3>With Defensive CSS</h3>
        <div class="flex-container with-defensive">
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
          <div class="flex-item"></div>
        </div>
      </section>
    </div>
  </main>
  <footer>
    <p>Linting Defensive & Logical CSS With Stylelint Plugins</p>
    <a href="https://twitter.com/DanielYuschick" aria-label="@Daniel Yuschick on Twitter">@DanielYuschick</a>
  </footer>
</div>
!

CSS 

              
                .flex-container {
  border: 1px solid var(--color-aux-100);
  display: flex;
  gap: var(--space-base-4x);
  overflow: hidden;
  max-inline-size: 100%;
  padding: 1em;

  .flex-item {
    background-color: var(--color-core-secondary);
    padding: var(--space-base-8x);
  }

  &.with-defensive {
    flex-wrap: wrap;
  }
}

/**********
*** SETUP
**********/
/***** Properties *****/
:root {
  --color-aux-50: rgb(10, 10, 11);
  --color-aux-100: rgb(29, 29, 32);
  --color-aux-200: rgb(48, 48, 54);
  --color-aux-300: rgb(77, 77, 86);
  --color-aux-400: rgb(96, 96, 108);
  --color-aux-500: rgb(115, 115, 130);
  --color-aux-600: rgb(147, 147, 159);
  --color-aux-700: rgb(169, 169, 178);
  --color-aux-800: rgb(190, 190, 197);
  --color-aux-900: rgb(223, 223, 226);
  --color-aux-950: rgb(242, 239, 233);

  --color-core-primary: #754abc;
  --color-core-secondary: #8b3257;

  --font-family-body: "Poppins", sans-serif;
  --font-family-heading: "Roboto Slab", serif;

  --space-base: 4px;
  --space-base-half: calc(var(--space-base) / 2);
  --space-base-1x: var(--space-base);
  --space-base-2x: calc(var(--space-base) * 2);
  --space-base-3x: calc(var(--space-base) * 3);
  --space-base-4x: calc(var(--space-base) * 4);
  --space-base-6x: calc(var(--space-base) * 6);
  --space-base-8x: calc(var(--space-base) * 8);
  --space-base-12x: calc(var(--space-base) * 12);
  --space-base-16x: calc(var(--space-base) * 16);
  --space-base-24x: calc(var(--space-base) * 24);
}

/***** Landmarks *****/
body {
  background-image: linear-gradient(
    335deg,
    hsl(263deg 46% 51%) 0%,
    hsl(263deg 44% 46%) 50%,
    hsl(263deg 46% 40%) 100%
  );
  padding: 1rem;
}

main {
  max-inline-size: 100vw;
  overflow: hidden;
}

footer {
  --padding-offset: var(--space-base-4x);

  align-items: center;
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
  justify-content: space-between;
  border-block-start: 1px solid var(--color-aux-50);
  padding-block: var(--padding-offset);
  margin-block-start: var(--padding-offset);
}

/***** Textual *****/
a,
a:visited,
a:active,
a:link {
  color: var(--color-core-secondary);
}

span,
p {
  font-family: var(--font-family-body);
}

p + p {
  margin-block-start: 1rem;
}

h1,
h2,
h3,
h4,
h5,
h6 {
  font-family: var(--font-family-heading);
}

code {
  background: var(--color-aux-100);
  color: var(--color-aux-950);
  display: block;
  padding: 0.25rem 0.5rem;

  &.inline {
    display: inline-block;
  }
}

/***** Other *****/
.content-container {
  inline-size: 75%;
  margin-inline: auto;
}

/**********
*** RESET
**********/
* {
  margin: 0;
  padding: 0;
}

*,
::before,
::after {
  box-sizing: border-box;
}

*:where(:not(fieldset, progress, meter)) {
  background-origin: border-box;
  border-style: solid;
  border-width: 0;
}

html {
  -webkit-text-size-adjust: none;
  block-size: 100%;
}

@media (prefers-reduced-motion: no-preference) {
  html:focus-within {
    scroll-behavior: smooth;
  }
}

body {
  -webkit-font-smoothing: antialiased;
  line-height: 1.5;
  min-block-size: 100%;
  text-rendering: optimizeSpeed;
}

:where(img, svg, video, canvas, audio, iframe, embed, object) {
  display: block;
}
:where(img, svg, video) {
  block-size: auto;
  max-inline-size: 100%;
}

:where(svg) {
  fill: currentColor;
  stroke: none;
}

:where(svg):where(:not([fill])) {
  fill: none;
  stroke-linecap: round;
  stroke-linejoin: round;
  stroke: currentColor;
}

:where(svg):where(:not([width])) {
  inline-size: 5rem;
}

:where(input, button, textarea, select),
:where(input[type="file"])::-webkit-file-upload-button {
  color: inherit;
  font-size: inherit;
  font: inherit;
  letter-spacing: inherit;
  word-spacing: inherit;
}

:where(textarea) {
  resize: block;
}

:where(span, p, h1, h2, h3, h4, h5, h6) {
  overflow-wrap: break-word;
  max-inline-size: 90ch;
}

:where(ul, ol) {
  list-style-position: inside;
}

:where(ul, ol, [role="list"]) {
  list-style: none;
}

:where(ul, ol, [role="list"]) li::before {
  border: 0px;
  clip: rect(0px, 0px, 0px, 0px);
  content: "\\200B";
  height: 1px;
  margin: -1px;
  overflow: hidden;
  padding: 0px;
  position: absolute;
  white-space: nowrap;
  width: 1px;
}

a:not([class]) {
  text-decoration-skip-ink: auto;
}

:where(a[href], area, button, input, label[for], select, summary, textarea, [tabindex]:not([tabindex*="-"])) {
  cursor: pointer;
  touch-action: manipulation;
}
:where(input[type="file"]) {
  cursor: auto;
}
:where(input[type="file"])::-webkit-file-upload-button,
:where(input[type="file"])::file-selector-button {
  cursor: pointer;
}

@media (prefers-reduced-motion: no-preference) {
  :focus-visible {
    transition: outline-offset 145ms cubic-bezier(0.25, 0, 0.4, 1);
  }
  :where(:not(:active)):focus-visible {
    transition-duration: 0.25s;
  }
}
:where(:not(:active)):focus-visible {
  outline-offset: 5px;
}

:where(button, button[type], input[type="button"], input[type="submit"], input[type="reset"]),
:where(input[type="file"])::-webkit-file-upload-button,
:where(input[type="file"])::file-selector-button {
  -webkit-tap-highlight-color: transparent;
  -webkit-touch-callout: none;
  text-align: center;
  user-select: none;
}

:where(button, button[type], input[type="button"], input[type="submit"], input[type="reset"])[disabled] {
  cursor: not-allowed;
}

/**********
*** UTILITIES
**********/
.content-container {
  min-block-size: calc(100vb - 2rem);
  inline-size: 100%;
  max-inline-size: 100vi;
  overflow: hidden;
  background-color: var(--color-aux-950);
  border: 1px solid bvar(--color-core-primary);
  border-radius: 4px;
  padding: 0 2rem;
  display: grid;
  grid-template-rows: min-content 1fr min-content;
}

.content-section {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-base-8x);
  align-items: start;
  padding-block: var(--space-base-8x);
  justify-content: space-between;
  overflow: hidden;
  max-inline-size: 100vi;
}

.demo {
  inline-size: max(calc(50% - var(--space-base-8x)), 500px);
}
!

JS
!
999px

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