# Getting Started

> Part of mCSS (mcss.dev). Rendered page: https://mcss.dev/docs/start

mCSS is both a CSS framework and a methodology. You need to first understand the methodology to use the framework correctly. There are 3 main parts to the methodology.

1. The file structure
1. The CSS syntax
1. The component architecture

Once you've read through the basics below, the best way to understand how it all comes together is to have a look at the [source code][src]. (Video tutorial coming soon!)

## mCSS file structure

<section class="docs_section prose">

The file structure is a simplified [ITCSS][1]: files are organized in [layers][layers] going from broad and generic (tokens, element defaults) to specific and local (components, one-off helpers). When done right, it takes care of all the common "shortcomings" of CSS such as [specificity][3] wars and cascading conflicts.

mCSS implements this with native [CSS cascade layers][cascade-layers]: every framework file is imported into a named `@layer`, and the layer order (not the import order or specificity) decides who wins. Anything you write _outside_ the layers beats the framework by default, so mCSS always gets out of your way. The only exception is [helper classes][helpers], which use `!important` so they can override anything, including your own CSS.

### Two folders

The styles live in two folders, and the split is the methodology in miniature:

- **[`framework/`][framework-src]**: mCSS itself, every file in a named layer. You copy it and mostly leave it alone: customization goes through the `settings.*` tokens, a [theme](/docs/themes), or your own CSS, not through edits scattered across framework files.
- **[`site/`][site-src]**: this site's own CSS, imported **unlayered, after the framework**, so it wins without specificity games. Because those files are unlayered, the order you import them in is important so make sure you have a clear mental model of [ITCSS][1] principles before delving in. You can also refer to mCSS [own `/site`'s setup][4] as a reference.

### The layers, in order

Each layer only ever loses to the ones after it. The sections below detail each one; most have full docs in the sidebar.

<div class="docs_oversizedTable">

| Layer         | Files         | What lives there                                         |
| ------------- | ------------- | -------------------------------------------------------- |
| `settings`    | `settings.*`  | Tokens, interface tokens, media queries, mixins          |
| `base`        | `base.*`      | Reset/normalize                                          |
| `elements`    | `elements.*`  | Default styling of bare HTML elements                    |
| `global`      | `global.*`    | Grid, wrap, layout scaffolds, prose, a11y                |
| `components`  | `component.*` | One self-contained block per file                        |
| `theme`       | `theme.*`     | At most one active theme (token overrides + style rules) |
| `helpers`     | `help.*`      | `!important` one-off overrides, last resort              |
| _(unlayered)_ | your own CSS  | Beats every layer above, except helpers                  |

</div>

Two entry files make the split concrete. The framework's own, [`framework/mcss.css`][mcss-entry], declares the layer order and puts every framework file in its layer. You never edit it:

```css
/* framework/mcss.css (abridged) */
@layer settings, base, elements, global, components, theme, helpers;

/* Build-time only (media queries + mixins definitions) */
@import url(./settings.media-queries.css);
@import url(./settings.mixins.css);

@import url(./settings.tokens.css) layer(settings);
@import url(./settings.ui.css) layer(settings);
@import url(./base.reset.css) layer(base);
@import url(./elements.text.css) layer(elements);
@import url(./global.grid.css) layer(global);
@import url(./component.button.css) layer(components);
@import url(./help.spacing.css) layer(helpers);
/* etc. */
```

Your site's entry (this site's is [`_global.css`][4]) pulls in the framework, activates at most one theme, then imports your own CSS unlayered:

```css
/* your entry file */
@import url(./framework/mcss.css);

/* Optional: activate ONE theme, a swappable style. Theme files are
   self-layered (@layer theme inside the file), so no layer()
   annotation. None imported = the default look. */
/* @import url(./framework/theme.wireframe.css); */

/* Your own CSS: UNLAYERED, after the framework. Its normal
   declarations win over every mCSS layer without fighting
   specificity. One exception: helpers are !important and beat
   unlayered CSS too. */
@import url(./site/global.layout.css);
@import url(./site/component.header.css);
@import url(./site/page.blog.css);
/* etc. */
```

[cascade-layers]: https://developer.mozilla.org/en-US/docs/Web/CSS/@layer
[mcss-entry]: https://github.com/minimaldesign/mCSS/blob/main/src/styles/framework/mcss.css

### How to import mCSS in your project

#### Drop-in file

Grab [`dist/mcss.css`][dist-css] (or [`dist/mcss.min.css`][dist-min]), the whole framework in one file, no build step needed. The easiest way to import, but the file size won't be optimized to your specific needs.

#### Individual files

Every framework file is also available pre-processed in [`dist/css/`][dist-dir] (with [`dist/css/mcss.css`][dist-index] as an `@import` index), so you can copy just the layers you need.

#### Source files

Copy [`src/styles/framework/`][framework-src] if you run PostCSS yourself (the source uses `@custom-media`, which needs [postcss-preset-env][presetEnv]).

Run `npm run build:css` in the repo to produce `dist/` from source.

[dist-css]: https://github.com/minimaldesign/mCSS/blob/main/dist/mcss.css
[dist-min]: https://github.com/minimaldesign/mCSS/blob/main/dist/mcss.min.css
[dist-dir]: https://github.com/minimaldesign/mCSS/tree/main/dist/css
[dist-index]: https://github.com/minimaldesign/mCSS/blob/main/dist/css/mcss.css
[framework-src]: https://github.com/minimaldesign/mCSS/tree/main/src/styles/framework
[site-src]: https://github.com/minimaldesign/mCSS/tree/main/src/styles/site

## Detailed description of each layer

<section class="docs_section prose">

### Settings

Settings are where all custom properties are set.

- [Tokens][5] is where you set default values for sizes, font stacks, colors, transitions, etc. See [the docs][5] for all the values available by default.
- [Interface tokens][interfaceTokens] are an abstraction level to standardize common values across elements and components. For instance, components use `--ui-border-color` instead of the lower level token `--base-200`, so one override restyles every bordered surface.
- [Media queries][6] include responsive sizes, as well as user preferences like color schemes, reduced motion, etc. See [media queries docs][6].
- **Mixins** is optional. It is not used in other parts of mCSS by default but can be useful to streamline your own components' code. It requires a [PostCSS plugin][7] to work.

### Base

- Simple reset/normalize.

### HTML Elements

The default styling of all HTML elements, without classes.

- **Sectioning:** `header`, `footer`, etc.
- **Text:** `a`, `p`, etc.
- **Quotes:** adds the correct quotes depending on language.
- **Media:** `img`,`video`, etc.
- **Table:** `table`, `th`, etc.
- **Form:** `input`, `button`, etc.
- **Interactive:** `dialog`, `details`.

### Global

Global styles included out of the box:

- A responsive [grid system][grid].
- A full feature [wrapper][wrap].
- Common global site [layouts][layout].
- [Typography][prose], via the `.prose` class, for long form text, like articles, etc.
- [Accessibility][a11y] (A11Y) specific classes.
- Basic `@keyframes` animations (e.g., fade in/out)

### Components

Self-contained styles for single components, one block per file. The mCSS framework is designed to be used on its own, allowing you to create your own components, but a [collection of components][components] built on top of mCSS is included.

Some components are **CSS-only**: a single class on a single element, with no Astro component because there is no markup structure to encapsulate. For example, the `.badge` class on a `<span>` is the whole badge, and the `.bt` class can style a `<button>` or an `<a>` (styling that has to be opt-in, since not all links are buttons). Their docs live in the [components section][components] like everything else, marked "CSS-only".

### Theme

This is the one layer the framework declares but never fills: `mcss.css` imports no theme, and the default look IS the empty theme layer. The theme itself is really part of [your CSS](#your-css-unlayered): one `theme.*.css` file of token overrides plus optional style rules that you activate from your own entry file, whether it's a shipped theme like `theme.wireframe.css` or one you wrote yourself. See [the theme docs][themes] for how themes work and how to build one.

### Helpers

[Helpers][helpers] provide classes for “one-off” local overrides. They're similar to utility classes from other frameworks, with a critical difference: they're meant to be used as a last resort and as sparingly as possible. Helper declarations use `!important`, and important declarations inside a layer beat unlayered CSS, so a helper class overrides everything on that element, including your own CSS. Read [the docs][helpers] for more info on this.

### Your CSS (unlayered)

Everything you write outside the mCSS layers (your components, page styles, and any third-party CSS you don't control) simply imports after the framework, unlayered. Unlayered CSS wins over all layered CSS for normal declarations, so you never fight the framework's specificity. The one exception is helper classes: their `!important` declarations win even over unlayered CSS.

It goes inside your `site/` folder, in this order:

- `theme.*.css` for your [theme][themes], at most one active. This is the one file of yours that is _not_ unlayered: a theme wraps its own content in `@layer theme`, deliberately dropping into the framework's theme slot so it restyles the framework defaults while the rest of your CSS below still beats it.
- `global.*.css` for site-wide additions to the framework's globals.
- `component.*.css` for your own blocks (most of your CSS should end up here)
- `page.*.css` for the rare page-specific styles
- `external.*.css` for CSS you don't control, ie. plugins

Because those files are unlayered, the order you import them in is important, so make sure you have a clear mental model of [ITCSS][1] principles before delving in. You can also refer to mCSS [own `/site`'s setup][4] as a reference.

**Page classes go on the `<body>`**, next to the [layout scaffold](/docs/global#layouts) classes, not on `<main>`:

```html
<body class="layout layout-centered blog blog-index"></body>
```

A page class is mostly a scope for token overrides, and tokens only inherit _down_: from the body they reach the whole scaffold, while a class on `<main>` can't touch anything above or beside it (`.layout_content`, the header, the footer). This site's blog index is the worked example: articles keep the default reading column, and one body class widens the listing page.

```css
/* page.blog.css */
.blog-index {
  --layout-content-width: 100%;
}
```

## mCSS classes syntax

<section class="docs_section prose">

Classes in mCSS are inspired by [BEM][bem], but they're simpler to use and easier to look at.

You can use standard BEM, the even more verbose [BEMIT][bemit], or any other syntax you'd like. But the mCSS syntax gets you 90% of the same benefits without any drawbacks, even on large projects involving many devs.

### Blocks, elements, and modifiers

<div class="docs_oversizedTable">

|          | BEM                  | mCSS               |
| -------- | -------------------- | ------------------ |
| Block    | `site-search`        | `siteSearch`       |
| Element  | `site-search__field` | `siteSearch_field` |
| Modifier | `site-search--full`  | `siteSearch-full`  |

</div>

### States

Here's how you implement a state in BEM vs. mCSS.

HTML:

```html
<!-- BEM -->
<form class="form">
  <input class="form__input" type="text" />
  <input class="form__submit form__submit--disabled" type="submit" />
</form>

<!-- mCSS -->
<form class="form">
  <input class="form_input" type="text" />
  <input class="form_submit is-disabled" type="submit" />
</form>
```

CSS:

```css
/* BEM */
.form__submit--disabled {
}

/* mCSS */
.form_submit {
  &.is-disabled {
  }
}
```

**One gotcha to keep in mind:** nesting a state inside its block compiles to a two-class selector (`.form_submit.is-disabled`), which beats single-class modifiers like `.form_submit-lg`. That's usually what you want: states describe what's happening _right now_, so they should win. But it means a state block is the wrong place to declare default values for custom properties. Declare defaults on the block itself, let modifiers override them, and only _use_ the properties inside the state. Otherwise your size and color modifiers will mysteriously stop working the moment the state class shows up.

```css
.avatar {
  /* ✅ defaults live on the block… */
  --status-dot-size: 12px;

  &.is-online {
    /* ❌ …not here: this would override .avatar-xl's dot size */
    &::after {
      /* ✅ states just consume the properties */
      width: var(--status-dot-size);
    }
  }
}

.avatar-xl {
  /* modifiers can now override the default */
  --status-dot-size: 20px;
}
```

## Components

<section class="docs_section prose">

### Targeting HTML elements within a component

When using mCSS syntax **within a component**, it's considered overkill to create a class for every single HTML element you need to target.

For example, this is acceptable (and recommended) CSS for the tags component (`component.tags.css`):

```css
.tags {
  li {
    […]
  }

  a {
    […]
    &:hover {
      […]
    }
  }
}
```

### Modifiers and component variations

When using modifiers to create different variations of a component, it's recommended to use local custom properties if possible instead of overriding the CSS directly.

```css
/* Don't do that */
.component {
  color: blue;
}

.component-variation {
  color: red;
}

/* Do that instead */
.component {
  --color: blue;
  color: var(--color);
}

.component-variation {
  --color: red;
}
```

See the [implementation][github] of the [notice component](/components/notice) for a real life example.

Any questions or feedback? Head over to the [Github discussions][discussions]!

## Browser support

<section class="docs_section prose">

mCSS targets **[Baseline](https://web.dev/baseline) 2024**: it freely uses cascade layers (`@layer`), nesting, `:has()`, `light-dark()`, `@scope`, `text-wrap: balance`, and relative color syntax, all natively, with no polyfills. In practice that means the current versions of Chrome, Edge, Firefox, and Safari, going back roughly two years.

How things degrade in older browsers:

- **Cascade layers, nesting, `:has()`** (2022–2023): load-bearing. Browsers without them are not supported.
- **`light-dark()`** (mid-2024): colors fall back to the light palette.
- **`@scope`** (mid-2024): only affects `.prose` internals; spacing between prose blocks and headings loses one refinement.
- **Scroll-driven animations**: the [ReadProgressBar](/components/readprogressbar) component detects support and falls back to JavaScript automatically.
- **`sibling-index()`, CSS `random()`, SVG displacement filters**: used only by the [wireframe theme](/docs/themes) for per-element sketch variation; without them the theme keeps its fixed hand-drawn look.

The exact compile floor lives in `.browserslistrc` (`defaults and supports css-cascade-layers`).

[1]: /blog/what-is-itcss
[2]: https://developer.mozilla.org/en-US/docs/Web/CSS/Syntax#css_rulesets
[3]: https://developer.mozilla.org/en-US/docs/Web/CSS/Specificity
[4]: https://github.com/minimaldesign/mCSS/blob/main/src/styles/_global.css
[5]: /docs/tokens
[6]: /docs/media-queries
[7]: https://github.com/postcss/postcss-mixins
[presetEnv]: https://github.com/csstools/postcss-plugins/tree/main/plugins/postcss-preset-env
[grid]: /docs/global#grid
[wrap]: /docs/global#wrap
[layout]: /docs/global#layouts
[prose]: /docs/global#prose
[a11y]: /docs/global#accessibility
[components]: /components/start
[helpers]: /docs/helpers
[interfaceTokens]: /docs/tokens#interface-tokens
[themes]: /docs/themes
[layers]: /blog/what-is-itcss#the-layers-of-itcss
[bem]: /blog/what-is-bem
[bemit]: https://csswizardry.com/2015/08/bemit-taking-the-bem-naming-convention-a-step-further/
[github]: https://github.com/minimaldesign/mCSS/blob/main/src/styles/framework/component.notice.css
[src]: https://github.com/minimaldesign/mCSS/tree/main/src/styles
[discussions]: https://github.com/minimaldesign/mCSS/discussions