Table of Contents
Why Styling Matters in Android Apps
Visual design is not only about making an app look pretty. In Android, styling and theming affect usability, consistency, and even how much work you do later when the design changes. Good use of styles and themes lets you change colors, typography, and common view attributes in a single place instead of editing dozens of XML files.
Styling and themes in Android act like a central design language for your app. Instead of repeating the same attributes in every layout, you describe them once and then apply them everywhere. This helps you keep your app consistent and reduces bugs that come from small visual differences between screens.
In this section of the course you will learn how Android organizes visual design into colors and dimensions, reusable styles, application wide themes, and support for dark mode. Each of those topics has its own chapter, so here you will focus on how they all relate to each other and how they form a coherent styling system.
A key rule: Do not hardcode visual values such as colors, text sizes, or margins directly into layout XML or code. Always prefer resources, styles, and themes. This makes your app easier to maintain, localize, and adapt to different devices and modes.
The Android Styling System at a Glance
Android uses several layers to define how your app looks. At the bottom you define simple values, then build more complex definitions on top of them.
At the lowest level you have resources like colors, dimensions, and fonts that live in XML files inside the res folder. These are just named values. Above them you create styles. A style is a collection of attributes, such as text color and text size, that you want to reuse for views. At the top you define themes. A theme is a style that applies to an entire activity or to the entire application. It can define high level design elements like primary colors, typography, and what variant of Material components your app uses.
You will also work with theme overlays, which are styles that temporarily change theme values in a small part of the screen. For example, you might have a light theme for your app but use a dark overlay for a bottom sheet. These overlays rely on the same theme system and keep the visual language consistent.
The result is a hierarchy where a single theme can supply default values for many attributes. Views can still override some of those values by referring to styles or specific resources, but the theme usually decides the general feeling of the app.
XML Based Styling vs Programmatic Styling
Android styles and themes are usually defined in XML. This is intentional. XML keeps design choices separate from code, so developers and designers can change the look of the app without touching business logic. For example, your layout XML might reference a style, and that style references colors and dimensions. None of your Kotlin code has to change when the design is updated.
You can also style views in code by calling methods like setTextColor or setBackgroundColor. While this is sometimes useful for dynamic situations, you should keep programmatic styling to a minimum. If you start changing many attributes in code, it becomes difficult to track and maintain the visual system of the app.
Whenever possible, you should rely on attributes defined in the theme. Many Material components automatically read values from the current theme, such as colorPrimary or colorOnPrimary. By configuring those attributes once, you affect all components that respect the theme without manually styling each one.
Consistency Through Reusable Styles
A central idea in Android styling is reuse. If you find yourself writing the same attributes on multiple views, that is usually a sign that you need a style. For example, suppose the main titles in your app are always bold, large, and of a certain color. Instead of repeating those attributes on every TextView, you define a style that contains those attributes and then apply that style.
This approach has several benefits. It reduces duplication, makes layouts easier to read, and allows quick global changes. If you later decide that your titles should be slightly larger, you change one style definition and the entire app updates.
Important principle: Layouts should describe structure and content, not design details. Design rules, such as font sizes and colors, should live in resources and styles so they can be shared and updated globally.
Themes as the Visual Identity of Your App
While styles are focused on individual views, themes express the identity of your whole app. A theme tells Android and its UI components which colors to use for backgrounds, which typography scale to prefer, and how widgets should behave visually.
Most modern Android apps use a Material theme descendant. This means they inherit from a base Material theme and then customize things like primary and secondary colors. Material components such as buttons, text fields, and cards look at the currently active theme to decide how they are drawn. If you configure your theme correctly, many views will look good by default without extra configuration.
You can apply themes at different levels. There is an application theme, which is declared in the manifest and acts as a default for all activities. Individual activities can override this theme by specifying a different one. Inside layouts, you can also apply themes to specific sections using theme overlays. This structure enables scenarios where one part of the screen uses an accent color or contrast different from the rest.
Having a coherent theme is especially important when you start to support features such as dark mode. If every view is individually colored, switching to a dark background will be painful. If your color choices come from theme attributes, you can provide alternative definitions for those attributes and the entire app will adapt automatically.
Designing for Multiple Devices and Modes
Styling in Android is always connected to the idea of flexibility. Your app might run on a small phone, a tablet, or even on a TV, and users can toggle dark mode or adjust font size. The styling system is designed to let your app respond to these changes without rewriting layouts.
Different resource files can be loaded automatically depending on device configuration. For example, you can provide different themes for night mode and day mode, and Android chooses the correct one depending on the system setting. You can also use qualifiers for screens with different densities or sizes to fine tune how your styles and dimensions behave.
By leaning on the resource system and theme attributes you prepare your app for different environments from the start. This is much easier than trying to retrofit support for larger screens or dark mode at the end of development.
Separation of Concerns Between Design and Logic
A significant benefit of learning styling and themes properly is separation of concerns. When visual definitions live in XML resources and themes, developers and designers can collaborate more effectively. A designer might adjust spacing, colors, or typography by modifying styles and themes without touching Kotlin classes.
In practice, this means you should aim for layouts that mostly reference styles, attributes, and resources, while your Kotlin code focuses on behavior, state, and interaction. If your code needs to adapt to theme values, it can look them up through the context, but those values still live in XML. This pattern is common when you use Material components in combination with architectural patterns like MVVM.
Guideline: Do not mix business logic with styling logic. Treat styles and themes as a separate layer that your UI components rely on, not as an afterthought embedded in code.
Evolution of Styling in Modern Android
Styling in Android has evolved over time, especially with the introduction of Material Design, Material Components, and newer toolkits like Jetpack Compose. Even though Compose uses a different system for theming in code, the core ideas are similar. You still define a consistent set of colors, typography, and shapes, and you still rely on themes instead of hardcoded values.
Understanding traditional XML based styles and themes remains important even as the ecosystem moves forward. Many apps will use a mix of Views and Compose, and both depend on the same resource system for many values. Learning the fundamentals here will prepare you to use both approaches with confidence.
Within this part of the course you will learn how to define and reference color and dimension resources, how to organize reusable styles, how to configure themes that affect your whole app, and how to add dark mode support that plays well with system settings and user preferences. Together these tools form the backbone of visual design in Android.