, the issue with your code is that you're trying to mix CSS modules and dynamic styles, but CSS modules don't really work that way. They're more for static, predefined class names. But no worries, there's a simple fix.

You can just use inline styles for dynamic stuff. Inline styles let you plug in your JavaScript values directly into your style attribute.

Here's what you can do:

In your Hero.js, instead of trying to attach your prop to a CSS module class, you can directly use it in a style object. Something like this:

const Hero = ({ heroHeight }) => {
 const dynamicStyle = {
 height: heroHeight, // This is where your dynamic height goes
 border: '1px solid green', // Assuming you always want this green border
};

 return (
  <div className={styles.pageWidth} style={dynamicStyle}>
   {/* Your Hero content */}
  </div>
 );
};

When you use your Hero component, just pass the height like you were doing:

<Hero heroHeight="400px" />

This is how you do it with vanilla CSS Modules

// vars.css
:root {
  --color-black: #222;
}


// myComponent.module.css
@import './vars.css';

.component {
  color: var(--color-black);
}

I would just use the default color vars on the element/body/whatever, then put the alternate theme colors in another class, and toggle the theme class via JS. Here's a demo.

$("button").on("click", function() {
  $("body").toggleClass("foo");
});

body {
  --red: red;
  --blue: blue;
  --yellow: yellow;
  background: #ccc;
  text-align: center;
  font-size: 5em;
}

.foo {
  --red: #ce1126;
  --blue: #68bfe5;
  --yellow: #ffd100;
}

.red {
  color: var(--red);
}

.blue {
  color: var(--blue);
}

.yellow {
  color: var(--yellow);
}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<span class="red">RED</span> <span class="blue">BLUE</span> <span class="yellow">YELLOW</span>
<br>
<button>click me</button>

I usually just define the style as an arrow function that returns the style object, and pass in whatever parameters are needed for the style. There is a shorthand notation for returning an object literal from an arrow function that works nicely for this.

const style = () => ({});

Just remember to only use ternary operators if using the shorthand, otherwise you would just need to explicitly return an object.

So, for your style:

const dropzoneStyle = (isPreview) => ({
  width: `200px`,
  height: `200px`,
  backgroundColor: `#1DA1F2`,
  backgroundImage: (isPreview) ? 'url(/path/to/image.jpg)' : 'none',
});

This adds the image is isPreview is true, but keeps it blank if not.

Then in your component, call the function where the style goes:

return (
  <div>
    <Dropzone
      {...otherProps}
      style={ dropzoneStyle(isPreview) }
    >
  </div>
);

Are you using CRA? If so, you can. You just have to make sure that you are using postcss and the postcss-modules-values plugin. NOTE: Haven't tested this without Create React App (yet), so if anyone has, it would help to know.

Now, all you need is create a stylesheet (or simply use the index.css, your choice), and do this:

@value blue: #0c77f8;
@value red: #ff0000;
@value green: #aaf200;

And now, from your component-scoped css file, just import and use (almost JS-like):

/* import your colors... */
@value colors: "./colors.css";
@value blue, red, green from colors;

.button {
  color: blue;
  display: inline-block;
}

Source(docs).

From the docs:

Avoid using multiple CSS Modules to describe a single element. https://github.com/gajus/react-css-modules#multiple-css-modules

@value colors: "../../styles/colors.css";
@value blue, black, red from colors;

.tile {
    position: relative;
    width: 100%;
    padding-bottom: 100%;
}

.black {
    composes: tile;
    background-color: black;
}

.blue {
    composes: tile;
    background-color: blue;
}

.red {
    composes: tile;
    background-color: red;
}

Then <div className={styles[this.props.color]} should do the job, e.g:

render: function(){
  // ES2015
  const className = styles[this.props.color];

  // ES5
  var className = '';

  if (this.props.color === 'black') {
    className = styles.black;
  }

  return (
    <div className={className}>
      {this.props.children}
    </div>
}

in case you need to use some js constants you can have a look at JSS which is a way to write css in js, you can integrate JSS in your react app using this guide

Like this:

function Component() {
  const style = { "--my-css-var": 10 } as React.CSSProperties;
  return <div style={style}>...</div>
}

Or without the extra style variable:

function Component() {
  return <div style={{ "--my-css-var": 10 } as React.CSSProperties} />
}