improve responsiveness container

[mattijn]

This PR can be tested using the following npm-test package

• https://www.npmjs.com/package/vega-embed-mattijn
• https://cdn.jsdelivr.net/npm/vega-embed-mattijn@6.

Further section is copied from: vega/altair#2867

---

Let me try to break this down.

Within Vega-Lite it is possible to define a fixed width and a container width. Altair uses Vega-Embed for rendering and if we like to support both the fixed width and container width in Altair then there are some changes required to the existing Vega-Embed css by overruling them.
The question is if these changes can be safely overruled or should they be made in Vega-Embed itself. What do you think @domoritz?

The breakdown is made by the following specification,

1. Chart width="container" (see gist) and
2. Chart width=200 (see gist)

import altair as alt
from vega_datasets import data

source = data.cars.url

alt.Chart(source, width='container').mark_circle(size=60).encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color='Origin:N',
).save('chart_container.html')

alt.Chart(source, width=200).mark_circle(size=60).encode(
    x='Horsepower:Q',
    y='Miles_per_Gallon:Q',
    color='Origin:N',
).save('chart_fixed.html')

---

Without changes to the .vega-embed CSS (before this PR) the charts will look like this:

(1) Chart width="container"

No width defined on parent, so chart width becomes 0.

(2) Chart width=200

Renders fine. Action button placed correctly

---

Defining .vega-embed to a width of 100%:

    .vega-embed {
      width: 100%;
    }

Results in:

(1) Chart width="container"

Responsive to the full width, but the open dialog of the action menu is to close to the right browser edge.

(2) Chart width=200

Chart renders fine on left-side, but the action button is placed on the right-side.

---

Overruling the following default css from Vega-embed (this PR):

    position: absolute;
    top: 0;
    right: 0;

With:

    .vega-embed {
      width: 100%;
      display: flex;
    }

    .vega-embed details,
    .vega-embed details summary {
      position: relative;
    }

Results in:

(1) Chart width="container"

Responsive width and action button on the right side, where the dialog is opened with a buffer on the right side.

(2) Chart width=200

Renders fine. Action button placed correctly

[mattijn]

Any good suggestions how I or others can support the review process?

[mattijn]

Let me add some comments while trying to assist in the review process.

I've tested it a bit with standard usage of vega-embed. Vega-embed works as usual with this PR when there is no custom overriding of the vega-embed css defaults.

But I noticed that some websites use custom css to override the vega-embed css defaults. One of these is streamlit.

Using tampermonkey and the following script I can see the effects of this PR at a particular website.

// ==UserScript==
// @name         New Userscript
// @namespace    http://tampermonkey.net/
// @version      0.1
// @description  Changes Vega charts' background color and style in Streamlit docs.
// @author       You
// @match        https://doc-vega-lite-chart.streamlit.app/~/+/?embed=true
// @icon         https://www.google.com/s2/favicons?sz=64&domain=streamlit.io
// @grant        none
// ==/UserScript==
(function() {
  'use strict';

  const observer = new MutationObserver((mutationsList, observer) => {
    const vegaElements = document.querySelectorAll('.vega-embed');

    if (vegaElements.length > 0) {
      observer.disconnect();

      vegaElements.forEach(vegaElement => {
        vegaElement.style.display = "flex";

        const detailObserver = new MutationObserver((mutationsList, observer) => {
          const detailsNode = vegaElement.querySelector('details');
          const summaryNode = vegaElement.querySelector('summary');

          if (detailsNode && summaryNode) {
            observer.disconnect();

            detailsNode.style.position = "relative";

            summaryNode.style.position = "unset";
            summaryNode.style.top = "unset";
            summaryNode.style.right = "unset";
          }

        })
        detailObserver.observe(document.body, {
          subtree: true,
          childList: true
        });
      });
    }
  });

  observer.observe(document.body, {
    subtree: true,
    childList: true
  });
})();

The script above only @match with https://doc-vega-lite-chart.streamlit.app/~/+/?embed=true

It seems there is defined a <button /> added outside the <div data-testid="stArrowVegaLiteChart" /> with an absolute position top right, therefor it is above the details.

If you know more sites that use vega-embed including usage of the actions, than I can test these as well.
If you think that this is proof enough already that this PR is too risky to be merged, fine as well.