sum()

Example

<div class="sum">
  <div>
    <i style="--value: 5"></i>
    <i style="--value: 1"></i>
    <i style="--value: 2"></i>
    <i style="--value: 3"></i>
    <i style="--value: 4"></i>
  </div>
  <b><output></output></b>
</div>

@property --result { syntax: '<integer>'; inherits: true; initial-value: 0; }
.sum output::after { counter-reset: result var(--result); content: counter(result); }
.sum { display: inline-grid; width: max-content; grid-template-columns: auto; }
.sum > div { display: flex; }
.sum > div > i { flex: none; width: calc(var(--value) * 1px); }
.sum > b { container-type: inline-size; }
.sum > b > output { --result: round(100cqw / 1px); }

dCSS Example

With dCSS, an element whose class is named after the function (dCSS’s docs).

<link rel="stylesheet" href="dcss.css">
<link rel="stylesheet" href="families/array.css">

<figure class="dcss-sum">
  <ul>
    <li style="--value: 5"></li>
    <li style="--value: 1"></li>
    <li style="--value: 2"></li>
    <li style="--value: 3"></li>
    <li style="--value: 4"></li>
  </ul>
  <output></output>
</figure>

Limits

These are the Example’s; the dCSS Example’s are in dCSS’s docs.

• values of 0 or more: calc() clamps a negative width to 0
• whole-number values, or halves and quarters: each width is laid out in 1/64 of a pixel in Chrome and WebKit and 1/60 in Firefox, so 256 values of 1/256 add up to 0
• no gap between the items: a gap adds to the sum
• the grid at its natural width (width: max-content): a grid stretched by its parent, as an item of a grid or of a column flexbox, stretches its auto columns, and the read with them
• a whole-number answer: the read rounds to 1px
• each answer under 1,000,000: from a million up, Chrome passes --result on as 1e+06, which counter-reset rejects, so the counter prints 0
• no margins, padding or borders on the items or the query containers: they add to the widths read, and 100cqw reads the content box
• each query container stretched across its track (justify-items and justify-self at their defaults): aligned to a side or the center, it shrinks to its content, none, and reads 0
• no other registration of --result on the page: a later @property --result that doesn’t inherit leaves the read right and the counter at 0

Browser support

Each row gives the first versions that support every feature its example uses, by MDN’s browser-compat-data. The Example was run in Chrome 155, Safari’s WebKit 26.4 and Firefox 158, the dCSS Example in Chrome 155 and Safari’s WebKit 26.4.