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

Borders are commonly used in most apps. This is one of the easier topics to talk about. We'll be talking about only two variables for borders:

- `--bd`: The normal border color.
- `--bd-focus`: The more stressed border color can be used on hover, for example.

# Using alpha channel

We'll use an alpha channel with either white or black to create our borders. We'll be using `rgba` again here:

- Light theme

```scss
// We're aiming for a simple transparent black border, so we set the alpha channel of black:
$bd-light: rgba(0, 0, 0, 0.1);
$bd-focus-light: rgba(0, 0, 0, 0.2);
```

- Dark theme

```scss
// We're aiming for a simple transparent white border, so we set the alpha channel of white:
$bd-dark: rgba(255, 255, 255, 0.1);
$bd-focus-dark: rgba(255, 255, 255, 0.2);
```

Some simple usages:

This lesson discusses how we'll deal with borders in our app.

Before Getting Started

Theory

Using css-theming

Samples

Borders

Using alpha channel