ListSubheader can no longer be styled to match the background color of dark-mode Paper components

Duplicates

• I have searched the existing issues

Latest version

• I have tested the latest version

Current behavior 😯

When using dark mode, if a List is created with ListSubheaders (that are sticky, the default) and placed inside of a Paper (or Card) component, the sticky headers cannot be made to match the background color of the Paper. This leads to an awkward-looking list, with inconsistent background colors:

One could change the entire List to have a different background-color than the Paper (and use that for the ListSubheaers), but that is also awkward/non-ideal, as that visually separates the list from everything else.

Expected behavior 🤔

It should be possible to consistently create a List with sticky subheaders where list items, list subheaders, and the rest of the paper all have the same background color.

Steps to reproduce 🕹

Demo:

https://codesandbox.io/s/pinnedsubheaderlist-material-demo-forked-0q1n4?file=/demo.js:438-448

Steps:

1. Set the theme to dark mode
2. Create a Paper component (with default elevation)
3. Put a List with ListSubheaders inside the Paper component
4. Observe that the background-color of the subheaders does not match the background-color of the Paper component or the rest of the list

Context 🔦

The main problem here is that in dark mode in MUI v5, elevated Paper does not use a fixed background-color, but rather uses a background-image to apply different color depending on the elevation (per https://github.com/mui-org/material-ui/pull/25522). ListSubheaders set background.paper as its background color: https://github.com/mui-org/material-ui/blob/a9903917f919092f80d84075f39fb51d51f241f2/packages/mui-material/src/ListSubheader/ListSubheader.js#L65

One would expect that you should be able to match the background color of the Paper so that all content within the List and the rest of the paper has the same background color. This is related to this other open issue, about styling custom components: https://github.com/mui-org/material-ui/issues/27980

Your environment 🌎

`npx @mui/envinfo`

Using Chrome.

This is on my system, but reproduced with CodeSandbox as well as linked above.

  System:
    OS: macOS 11.6
  Binaries:
    Node: 14.18.2 - ~/.nvm/versions/node/v14.18.2/bin/node
    Yarn: 1.22.10 - ~/repos/project/frontend/node_modules/.bin/yarn
    npm: 6.14.15 - ~/.nvm/versions/node/v14.18.2/bin/npm
  Browsers:
    Chrome: 96.0.4664.110
    Edge: Not Found
    Firefox: 91.0.1
    Safari: 15.0
  npmPackages:
    @emotion/react: ^11.7.1 => 11.7.1
    @emotion/styled: ^11.6.0 => 11.6.0
    @mui/base:  5.0.0-alpha.62
    @mui/icons-material: ^5.2.5 => 5.2.5
    @mui/lab: ^5.0.0-alpha.62 => 5.0.0-alpha.62
    @mui/material: ^5.2.6 => 5.2.6
    @mui/private-theming:  5.2.3
    @mui/styled-engine:  5.2.6
    @mui/styles: ^5.2.3 => 5.2.3
    @mui/system: ^5.2.6 => 5.2.6
    @mui/types:  7.1.0
    @mui/utils:  5.2.3
    @mui/x-data-grid: ^5.2.1 => 5.2.1
    @types/react: ^17.0.19 => 17.0.19
    react: ^17.0.2 => 17.0.2
    react-dom: ^17.0.2 => 17.0.2
    typescript: ^4.4.3 => 4.4.3

[sjdemartini]

@lucianthorr My hacky workaround for now is that I’ve added the following constant to my project:

// Paper components in dark mode in MUI v5 use a background-image to set the background "color"
// depending on the elevation of the Paper. As such, choosing `palette.background.paper` in dark
// mode will *not* match the paper background color if using elevation (the default). This is the
// color that matches the background-image's color when the total elevation is 1 (the Paper is on
// top of only the default background, with elevation=1), which is useful if we need "sticky" header
// placement in a scrolling container.
export const DARK_MODE_PAPER_BACKGROUND_COLOR_ELEVATION_1 = "#1e1e1e";

and then I use this as the backgroundColor for whatever element I need (typically a position: sticky element), like

    // We match the Paper elevation background in dark mode by using the
    // explicit color, since background.paper will *not* match
    backgroundColor:
      theme.palette.mode === "dark"
        ? DARK_MODE_PAPER_BACKGROUND_COLOR_ELEVATION_1
        : theme.palette.background.paper,

Don’t love it, but it let me unblock the v4->v5 MUI upgrade.

[tomkontra]

@sjdemartini @lucianthorr A slightly cleaner workaround would be to replicate what Paper does and add a semi-transparent background image to the ListSubHeader.

export const OVERLAY_ALPHA = 0.16

// Based on implementation of Paper component at: 
// https://github.com/mui/material-ui/blob/master/packages/mui-material/src/Paper/Paper.js
backgroundImage: `linear-gradient(${alpha('#fff', OVERLAY_ALPHA)}, ${alpha('#fff', OVERLAY_ALPHA)})`

You can either use a const for the alpha value or copy the getOverlayAlpha function from Paper.js:

export const getOverlayAlpha = (elevation) => {
  let alphaValue;
  if (elevation < 1) {
    alphaValue = 5.11916 * elevation ** 2;
  } else {
    alphaValue = 4.5 * Math.log(elevation + 1) + 2;
  }
  return (alphaValue / 100).toFixed(2);
};

Saves having to figure out the different colors that result from applying the overlay.