Gain insights into practical CSS theming methods, delve into problem-solving, and discover the css-theming package to create highly customizable, dark mode-friendly apps in this course.

CSS isn’t what it used to be. Today, you’ll be hard-pressed to find a strong, straightforward, and expressive UI language that can beat modern CSS. As the tech world moves more and more towards web-based frameworks for UI, we start to see a bigger emphasis on highly customized looks for apps.

In this course, you'll learn how to properly develop apps that are theme aware. This course is split into two sections: in the first section, you will learn the practical methods and patterns around theming and discover common problems and their solutions. In the second section, you will get hands-on experience with the css-theming package and through it you'll learn how to customize every facet of your app. Most importantly, no matter the kind of app you're developing, users have come to expect dark mode support nowadays as a given.

By the end of this course you’ll be able to create stunning apps that are highly customizable by either applying what you learned in your own way or using the css-theming package.

CSS Theming for Professionals

# What is programmatic access?

As developers who use web technologies, we're used to working across three different but cooperative languages: HTML (the layout), JS (the script), CSS (the style).

Sometimes, it's beneficial to be able to access what we define in CSS from the script. This is what we mean by gaining programmatic access to the values we define in our CSS/SCSS.

Let's look at a use case. Assuming we have 3 different themes in our app, we'll have those defined somewhere in our CSS/SCSS files. It's a common need to display some kind of page where the end user can select what theme they want. In such a case, we'll want a way for our code to get the names of those themes. We _could_ put the theme names in our code file in addition to their definitions in CSS/SCSS, but that would be redundant and will double the places we'll have to edit if we ever change anything.

What we need is a way to obtain the different CSS values we're defining in CSS programmatically.

# Explanation

In JavaScript, we do this by obtaining the computed styles of an element:

```javascript
const style = getComputedStyle(element);
const value = style.getPropertyValue(prop);
```

The `prop` above can be any CSS prop or CSS variables. Our strategy here is to somehow put the theme names in a CSS variable.

Let's assume we have our themes defined as a SCSS `map`:

```scss
$themes: (
  'light-theme': (...),
  'dark-theme': (...)
);
```

To get a list of the theme names we'll map the keys to obtain a list of the names:

```scss
$theme-names: map-keys($themes);
```

Then, put the result in a CSS variable so that we can obtain it later in code:

```scss
body {
  --theme-names: #{$theme-names};
}
```

The `--theme-names` variable will contain a comma delimited list of the names now.

Then, obtaining those names in code becomes easy:

```javascript
const style = getComputedStyle(document.body);
const names = style.getPropertyValue('--theme-names');
const themeNames = names.split(',').join(', ');
```

Putting all of this together:

This lesson discusses how to have programmatic access to all the data we define in CSS.

Before Getting Started

Theory

Using css-theming

Samples

Programmatic Access

What is programmatic access? #