Introduction > Themes

With Feo CSS it is possible to define multiple themes. Within a theme, color-based custom properties are generated. In $feo-themes you define lists similar to $feo-colors. The difference, however, is that you don't set the color, but you set a reference to a color in $feo-colors, as shown below. This results in themes being created that can be applied using data-theme on elements.

If you have a duplicate name between $feo-colors and $feo-themes, the $feo-colors one will take precedence.

The generated custom properties are defined in a data-theme scoping. The chosen theme in data-theme will only be applied to all children of the element it is applied to. It is not applied to the entire page, unless you apply data-theme on the html or body tags.

scss$feo-themes: (
    'dark': (
        'back': 'black',
        'front': 'white'
    )
);

[data-theme='{theme-name}'] {
    --color-back: var(--color-black);
    --color-front: var(--color-white);

    //Only for 'light' and 'dark' themes
    color-scheme: 'dark'/'light';
}

.bg-back {
    background-color: var(--color-back);
}

The utility classes are generated based on the first defined theme. If not all themes have the same colors defined, you will miss utility classes, or classes will be broken.

User preference

For themes called 'dark' or 'light', system preferences are taken into account as well. When no data-theme is set, it will fall back to the system prefered color scheme. This is achieved with a prefers-color-scheme @media query. Below an example of the dark theme if the running example.

scss@media (prefers-color-scheme: dark) {
    :root:not([data-theme]) {
        --color-back: var(--color-black);

        color-scheme: dark;
    }
}