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Set CSS value in HTML to reflect current theme #192

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vsajip opened this issue Jul 1, 2024 · 5 comments
Open

Set CSS value in HTML to reflect current theme #192

vsajip opened this issue Jul 1, 2024 · 5 comments
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enhancement help wanted

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@vsajip
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vsajip commented Jul 1, 2024

See this page, where the anchor points to an SVG. If you ensure that there's no theme in local storage for this page, then if the browser settings are used to switch between dark and light modes (I'm using Firefox), the SVG is styled appropriately to display correctly. However, if I use the theme selector on the page to select dark mode when the browser is set to light mode, the SVG does not display correctly.

The reason is that I style for light mode and use a media query to override some styles, using @media (prefers-color-scheme: dark). However, when the theme selector is used to select dark mode, then some dark-mode CSS is pulled in using the activateTheme() JS function, but from what I can tell this leaves no trace in the markup that we're now in dark mode. If there were e.g. a dark-theme class added to the <body> tag when the page is in dark mode, then I could duplicate the styling using an appropriate selector. My complete styling of the SVG is:

    svg {
      background-color: transparent !important;
    }
    line {
      stroke: #000000;
      fill: none;
      stroke-opacity: 1;
    }
    polygon, rect {
      fill: none;
      stroke: #000000;
      fill-opacity: 1;
      stroke-opacity: 1;
    }
    polygon.filled {
      fill: #ff0000;
    }
    polyline {
      fill: none;
      stroke-opacity: 1;
      stroke: #000000;
    }
    text {
      fill: #000000;
      fill-opacity: 1;
      stroke: none;
      font-family: sans-serif;
      font-style: normal;
      font-weight: normal;
      text-anchor: start;
    }
    @media (prefers-color-scheme: dark) { /* could duplicate this styling if body.dark-theme */
      polygon, rect, polyline, line {
        stroke: #ffffff;
      }
      text {
        fill: #ffffff;
      }
    }

If there is another approach I could use to achieve the desired result (proper styling of the SVG in all cases), please let me know. Otherwise, would you consider adding dark-theme class to the body or other container tag so that I could try and achieve the desired result? Or have I missed somewhere where such a class has been added?
@vsajip vsajip added the question label Jul 1, 2024
@vsajip
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vsajip commented Jul 3, 2024

I got this working by overwriting activateTheme with my own function, see here. The result can be previewed here. It would still be good to have the function of setting/unsetting body.{light,dark}-theme in this theme.

@hugovk hugovk changed the title SVG created to work in dark and light mode works as expected when using the browser to set the mode, but not when using the theme selector Set CSS value in HTML to reflect current theme Jul 21, 2024
@hugovk
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hugovk commented Jul 21, 2024

Yeah, https://peps.python.org/ has a data-colour_scheme attribute on the html element that changes between dark, light and auto based on the theme selection.

I'd welcome a PR to do something like this here too.

@vsajip
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vsajip commented Jul 22, 2024

Do you want it to match the peps.python.org behaviour exactly? Or is what I've implemented (using the body tag, and the attribute has a -theme suffix) OK?

@hugovk
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hugovk commented Jul 22, 2024

We don't need to copy peps.python.org exactly.

Checking a couple of others:

Furo has a <body data-theme="dark"> which toggles the three states.

PyData Sphinx Theme has the same thing, but it only togges light and dark. It also has a data-mode that toggles the thee states.

Hmm, shall we follow Furo?

@pradyunsg
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pradyunsg commented Jul 22, 2024 •
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I'd suggest following PyData Sphinx Theme honestly -- Furo's approach works because of the weird stacking it has due to the legacy of being a light-only theme that evolved a dark mode and requires... shenanigans (see https://github.com/pradyunsg/furo/blob/main/src/furo/assets/styles/base/_theme.sass which includes dark colors twice).

PyData's approach allows content to only care about the current display theme, with keeping relevant "what mode is selected" state separately, which would work better for the usecases like showing the dark mode SVG when content is dark.

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