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CSS

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CSS Base

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HTML 

              
                <header>
  <h1>Demo of line using height units for paragraph margins</h1> 
</header>

<main>  
  <section class="demo paragraphs-demo">
    <h2>Paragraphs</h2>
    <div class="interface">
      <label class="margins" for="paragraphs-margins">margin-block<span>:</span>
        <select name="paragraphs-margins" id="paragraphs-margins">
          <option value="one-line-height">1lh<span>;</span></option>
          <option value="one-em">1em<span>;</span></option>
          <option value="zero">0<span>;</span></option>
        </select>
      </label>
      <label class="margins" for="margin-trim">margin-trim<span>:</span>
        <select name="margin-trim" id="margin-trim">
          <option value="margin-trim-none">none<span>;</span></option>
          <option value="margin-trim-block">block<span>;</span></option>
          <option value="margin-trim-block-start">block-start<span>;</span></option>
          <option value="margin-trim-block-end">block-end<span>;</span></option>
        </select>
      </label>
      <label for="font-paragraphs">Font:  
        <select name="font-options" id="font--headline-image">
          <option value="old-style">Old Style</option>
          <option value="system-ui">System UI</option>
          <option value="transitional">Transitional</option>
          <option value="humanist">Humanist</option>
          <option value="geometric-humanist">Geometric Humanist</option>
          <option value="classical-humanist">Classical Humanist</option>
          <option value="neo-grotesque">Neo-Grotesque</option>
          <option value="monospace-slab-serif">Monospace Slab Serif</option>
          <option value="monospace-code">Monospace Code</option>
          <option value="industrial">Industrial</option>
          <option value="rounded-sans">Rounded Sans</option>
          <option value="slab-serif">Slab Serif</option>
          <option value="antique">Antique</option>
          <option value="didone">Didone</option>
          <option value="handwritten">Handwritten</option>
        </select>
      </label>  
      <label for="margin-guides" class="margins">Show margins: 
        <input type="checkbox" switch id="margin-guides">
      </label>
      <label for="line-grid" class="line-grid">Show line grid: 
        <input type="checkbox" switch id="line-grid">
      </label>
      <aside class="margin-trim-support"><p>(This browser does not support <code>margin-trim</code>. Try this demo in Safari, or another <a href="https://caniuse.com/mdn-css_properties_margin-trim" target="_blank">browser that does</a>.)</p></aside>
    </div>
    <article class="paragraphs">
      <div> <!--just-for-the-guides-->
      <p>Lorem ipsum dolor sit amet, similique moderatius sea ex. Te assum principes mea. Illum suavitate vis no, cu utroque nonumes accusamus vix. Impetus officiis vim et, eu discere delicata mel. His te malis tantas. An probo omnium cotidieque sed, nec dicat blandit et, mucius feugait vivendum per id.</p>
      <p>Ut eum posse alterum, commodo instructior ne nec. Vero viris ut vel, id salutatus constituam ius. Suscipit persecuti te ius, id quem ridens eam, quo te fugit torquatos elaboraret. Mei ex doctus recteque iudicabit. Blandit deserunt cu vis, his et atqui homero. Erat dissentiet voluptatibus ex vis, et omnis honestatis pro.</p>
      <p>Eu quando inermis usu, qui magna illum in. Qui idque primis id. Cu luptatum perfecto ius, mel ne soluta offendit, quo viris fastidii in. An affert utamur theophrastus pro. Id impedit molestie accusata vel, te vix ridens gubergren liberavisse.</p>
      <p>Mea te theophrastus contentiones. At vix populo propriae. Eros volumus splendide ex vis. Modus incorrupte ut his. Ex duo modus mazim eirmod. Quo detracto complectitur an, ad qui postea dissentiunt.</p>
      <p>Sea et debitis torquatos scriptorem. Ut euismod feugait convenire vix, vim quem consetetur intellegebat te. Mel an noster persius vocibus, no vix rebum omittantur complectitur, cu est quot doming scriptorem. Sit ne malis lobortis argumentum, per et illum ridens adipiscing, eum at sale necessitatibus. Nusquam aliquando accommodare in cum, sed simul timeam ne.</p>
      <figure class="grid-lines">
        <hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr><hr>
      </figure>
     </div>
    </article>
  </section>  
</main>
!

CSS 

              
                /*-------------------------------------------*/
/*   Options                                 */
/*-------------------------------------------*/

/* Margin block */

section:has(option[value="zero"]:checked) article p {
  margin-block: 0;
}
section:has(option[value="one-em"]:checked) article p {
  margin-block: 1em;
}
section:has(option[value="one-line-height"]:checked) article p {
  margin-block: 1lh;
}

/* Margin trim */

section:has(option[value="margin-trim-none"]:checked) article div {
  margin-trim: none;
}
section:has(option[value="margin-trim-block"]:checked) article div {
  margin-trim: block;
}
section:has(option[value="margin-trim-block-start"]:checked) article div {
  margin-trim: block-start;
}
section:has(option[value="margin-trim-block-end"]:checked) article div {
  margin-trim: block-end;
}

/* Support note about margin-trim */

.margin-trim-support {
  display: none;
  font-size: 85%;
  line-height: 1.4;
  background: light-dark(rgb(255, 0, 0, 0.2), rgb(140, 63, 95));
  margin-block: 1lh;
  padding: 1px 1lh;
  a {
    color: light-dark(black, #f5abca);
  }
}
section:has(option[value="margin-trim-block"]:checked) {
  @supports not (margin-trim: block) {
    .margin-trim-support {
      display: block;
    }
  }
}


/*-------------------------------------------*/
/*   Paragraphs and Guides                   */
/*-------------------------------------------*/

.paragraphs {
  p {    
    font-size: 1.2rem;
    line-height: 1.3;
  }
}
.paragraphs div {
  border: 1px solid canvas;
}
body:has(input[id="margin-guides"]:checked) {
  .paragraphs {
    background-color: light-dark(lemonchiffon, midnightblue);
    div {
      background-color: light-dark(rgb(0, 232, 232, 0.3), 
                        color(display-p3 0 0.431 0.435));
    }
    p {
      background-color: canvas;
    }
  }
}

/*-------------------------------------------*/
/*   Line Grid                               */
/*-------------------------------------------*/

.grid-lines {
 display: none; 
}
body:has(input[id="line-grid"]:checked) {
  .grid-lines {
    width: 100%;
    height: calc(100% + 1px);
    margin: 0;
    padding: 0;
    display: block;
    position: absolute;
    top: 0;
    left: 0;
    overflow: hidden;
    hr {
      margin: 0;
      padding: 0;
      width: 100%;
      height: 1lh;
      border: 0;
      border-block: 0.5px solid light-dark(#00e8e8, 
                        color(display-p3 0 0.634 0.64));
    }
    hr:nth-child(1) {
      border-block-start-width: 1px;
    }
  }
}




/*-------------------------------------------*/
/*   Overall page and UI                     */
/*-------------------------------------------*/

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

:root {
  color-scheme: light dark;
  --code-font: ui-monospace, 'Cascadia Code', 'Source Code Pro', Menlo, Consolas, 'DejaVu Sans Mono', monospace;
  --code-color: rebeccapurple;
}
body {
  margin: 4rem;
  font-family: ui-rounded, system-ui, sans-serif;
  background: light-dark(#f0ebd4, color(display-p3 0.181 0.235 0.059));
}
header {
  text-align: center;
  color: light-dark(green, hotpink);
  code { color: green;  font-family: inherit; }
  h1 { 
    font-size: 3.2rem; 
    margin: 0; 
    font-weight: 100;
    text-wrap: balance;
  }
}
code {
  color: var(--code-color);
  font-family: var(--code-font);
}
main {
  display: grid;
  gap: 4rem;
  margin-block-start: 3rem;
  margin-inline: auto;
  max-width: 1250px;
}
main, button {
  font-family: var(--font-family);
} 
section.demo {
  display: grid;
  grid-template-columns: 32ch 1fr;
  grid-template-rows: max-content 1fr;
  grid-template-areas: "header demo"
                       "interface demo";
  gap: 2rem 1rem;
  background: light-dark(#faf6e3, #c8bf93);
  align-items: start;
  > h2 {
    grid-area: header;
    font-size: 1.8rem;
    font-weight: 100;
    color: #6e5b45;
    margin: 0;
    padding: 2rem 0 0 2rem;
  }
  .interface {
    grid-area: interface;
    padding: 0 0 2rem 2rem;
    /* should be padding-inline-start: 2rem; for narrow screens*/
    font-family: var(--code-font);
    label, select { color: var(--code-color); }
    label { display: block; margin-block-end: 0.5lh;}
    span { color: black; } 
    .guides {
      display: flex;
      align-items: center;
      gap: 0.5lh;
      accent-color: var(--code-color);
    }
  }
  article div {
    position: relative;
  }
  article {
    grid-area: demo;
    background: canvas;
    color: textColor;
    padding: 2lh;
    width: 100%;
    align-self: stretch;
    align-items: center;
    font-size: 1.2rem;
    line-height: 1.3;
  }
}
@media (max-width: 800px) {
  body {
    margin: 1.5rem;
  }
  header {
    h1 { 
      font-size: 1.8rem; 
    }
  }
  main {
    margin-block-start: 1.5rem;
  }
  section.demo {
    grid-template-columns: 1fr;
    grid-template-rows: auto;
    grid-template-areas: "header"
                         "interface"
                         "demo";
    .interface {
      padding: 0 0 0 2rem;
    }
    article {
      padding: 1lh;
    }
  }
}
select {
  appearance: none;
  width: auto;
  margin: 0;
  padding: 0.25em 0.5em;
  font-family: inherit;
  font-size: inherit;
  line-height: inherit;
  cursor: pointer;
  background-color: rgb(255, 255, 255, .5);
  background-image: linear-gradient(to top, rgb(0, 0, 0, 0.03), rgb(255, 255, 255, 0) 50%);
  border: 1px solid #ebe7e2;
  border-radius: 0.25em
}


/*-------------------------------------------*/
/*   Font Options                            */
/*-------------------------------------------*/

/* Thanks modernfontstacks.com for the font stacks! */

section article {
  font-family: var(--font-family);
}
section:has(option[value="system-ui"]:checked) {
  --font-family: system-ui, sans-serif;
}
section:has(option[value="transitional"]:checked) {
  --font-family: Charter, 'Bitstream Charter', 'Sitka Text', Cambria, serif;
}
section:has(option[value="system-ui"]:checked) {
  --font-family: system-ui, sans-serif;
}
section:has(option[value="system-ui"]:checked) {
  --font-family: system-ui, sans-serif;
}
section:has(option[value="transitional"]:checked) {
  --font-family: Charter, 'Bitstream Charter', 'Sitka Text', Cambria, serif;
}
section:has(option[value="old-style"]:checked) {
  --font-family: 'Iowan Old Style', 'Palatino Linotype', 'URW Palladio L', P052, serif;
}
section:has(option[value="humanist"]:checked) {
  --font-family: Seravek, 'Gill Sans Nova', Ubuntu, Calibri, 'DejaVu Sans', source-sans-pro, sans-serif;
}
section:has(option[value="geometric-humanist"]:checked) {
  --font-family: Avenir, Montserrat, Corbel, 'URW Gothic', source-sans-pro, sans-serif;
}
section:has(option[value="classical-humanist"]:checked) {
  --font-family: Optima, Candara, 'Noto Sans', source-sans-pro, sans-serif;
}
section:has(option[value="neo-grotesque"]:checked) {
  --font-family: Inter, Roboto, 'Helvetica Neue', 'Arial Nova', 'Nimbus Sans', Arial, sans-serif;
}
section:has(option[value="monospace-slab-serif"]:checked) {
  --font-family: 'Nimbus Mono PS', 'Courier New', monospace;
}
section:has(option[value="monospace-code"]:checked) {
  --font-family: ui-monospace, 'Cascadia Code', 'Source Code Pro', Menlo, Consolas, 'DejaVu Sans Mono', monospace;
}
section:has(option[value="industrial"]:checked) {
  --font-family: Bahnschrift, 'DIN Alternate', 'Franklin Gothic Medium', 'Nimbus Sans Narrow', sans-serif-condensed, sans-serif;
}
section:has(option[value="rounded-sans"]:checked) {
  --font-family: ui-rounded, 'Hiragino Maru Gothic ProN', Quicksand, Comfortaa, Manjari, 'Arial Rounded MT', 'Arial Rounded MT Bold', Calibri, source-sans-pro, sans-serif;
}
section:has(option[value="slab-serif"]:checked) {
  --font-family: Rockwell, 'Rockwell Nova', 'Roboto Slab', 'DejaVu Serif', 'Sitka Small', serif;
}
section:has(option[value="antique"]:checked) {
  --font-family: Superclarendon, 'Bookman Old Style', 'URW Bookman', 'URW Bookman L', 'Georgia Pro', Georgia, serif;
  --font-family: Superclarendon, monospace;
}
section:has(option[value="didone"]:checked) {
  --font-family: Didot, 'Bodoni MT', 'Noto Serif Display', 'URW Palladio L', P052, Sylfaen, serif;
}
section:has(option[value="handwritten"]:checked) {
  --font-family: 'Segoe Print', 'Bradley Hand', Chilanka, TSCu_Comic, casual, cursive;
}
!

JS
!
999px

Console