Custom Themes

👋 Welcome to theme()

The theme() function in ggplot2 lets you control the non–data parts of a plot—things like titles, axis labels, legends, grid lines, and background.

While built-in themes give you quick presets, theme() provides full flexibility: you can adjust individual elements (like an axis label or a margin) to make your chart match your style or branding.

Think of it as the fine-tuning tool for your plot’s appearance.

Let's start with a simple example. What if we want to change the plot panel background color:

🦴 Anatomy of a Theme

The theme() function lets you override ggplot2’s default theme elements.

You pass arguments to theme(), where each argument corresponds to a specific element: a part of the plot you want to customize. For example, above we modified the plot’s panel background by changing the panel.background element:

The value you assign to an element must be an element function. In this case, we use element_rect(), the function designed for elements drawn as rectangles.

element_rect() accepts several attributes such asfill, color, and linewidth. To customize an attribute, you simply provide a value for it.

✋ The 5 Types of Element Functions

The plot panel is a rectangle, so we used the element_rect() function. To modify text labels, however, we would use element_text().

In fact, ggplot2 provides five different element functions, each designed for a specific kind of component:

• element_blank() – removes the element entirely
• element_rect() – for rectangular shapes like backgrounds
• element_line() – for lines such as axes or grid lines
• element_text() – for text elements like titles and labels
• element_grob() – for inserting custom grid graphics (rarely used)

🔍 Theme Attribute Explorer

Plot elements in ggplot2 are organized into five main groups. Each group contains many arguments, forming a fairly deep hierarchy.