How can LessCSS be used to define and apply dynamic themes for web applications?

Thematizing in LessCSS

In the preproduction stages of app development, experimenting with various visual themes is essential. To facilitate this, defining global Less variables that can be dynamically themed based on CSS class can be useful.

Defining Themed Variables

To define variables that can change depending on an appearance class, you can use Less's nesting and inheritance features. For example:

// default appearance
@navBarHeight: 50px;

.appearanceWhite {
    @navBarHeight: 130px;
}
.appearanceBlack {
    @navBarHeight: 70px;
}

Applying Themes to Elements

Once the variables are defined, you can use Less's class nesting to apply different styles based on the appearance class:

#navBar {
    height: @navBarHeight;

    // appearance handling
    .appearanceBlack & {
        background-color: black;
    }
    .appearanceWhite & {
        background-color: white;
    }
}

Advanced Theming

For more complex cases, you can utilize Less's features like Pattern Matching and Ruleset Arguments. For example, using the @for loop:

@themes:
    blue   rgb( 41, 128, 185),
    marine rgb( 22, 160, 133),
    green  rgb( 39, 174,  96),
    orange rgb(211,  84,   0),
    red    rgb(192,  57,  43),
    purple rgb(142,  68, 173);

.themed(@property) {
    .for(@themes); .-each(@theme) {
        @name:  extract(@theme, 1);
        @color: extract(@theme, 2);

        .theme-@{name} & {
            @{property}: @color;
        }
    }
}

Conclusion

By defining and applying themed variables, developers can easily experiment with different visual themes in Less. Utilizing advanced features enables the creation of complex appearance hierarchies and dynamic style generation.

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