The shimmer utility is purely composed of CSS and is based on shadcn/shimmer. No extensions to rxconfig.py are needed as it uses Tailwind v4 syntax.

If your project was set up with buridan init, you already have shimmer. It ships with the buridan package, which the CLI imports in your global CSS file.

Otherwise install the buirdan package:

uv run buridan init

You can also copy paste the shimmer source directly into your globals.css file. Make sure you also include the correct imports, such as @tailwind utilities; at the top of your CSS file.

@property --shimmer-angle {
    syntax: "<angle>";
    inherits: true;
    initial-value: 20deg;
}
@property --shimmer-image {
    syntax: "*";
    inherits: false;
}
@property --shimmer-text-fill {
    syntax: "*";
    inherits: false;
}

@theme inline {
    @keyframes tw-shimmer {
        from {
            background-position: 100% 0;
        }
        to {
            background-position: 0 0;
        }
    }
}

@utility shimmer {
    --_spread: var(--shimmer-spread, calc(3ch + 40px));
    --_base: currentColor;
    --_highlight: var(
        --shimmer-color,
        oklch(from currentColor l c h / calc(alpha* 0.2))
    );

    background-image: var(
        --shimmer-image,
        linear-gradient(
            calc(90deg + var(--shimmer-angle)),
            var(--_base) calc(50% - var(--_spread)),
            color-mix(in oklch, var(--_highlight), var(--_base) 50%)
                calc(50% - var(--_spread) * 0.5),
            var(--_highlight) 50%,
            color-mix(in oklch, var(--_highlight), var(--_base) 50%)
                calc(50% + var(--_spread) * 0.5),
            var(--_base) calc(50% + var(--_spread))
        )
    );
    background-repeat: no-repeat;
    background-size: calc(200% + var(--_spread) * 2) 100%;
    background-position: 0 0;
    background-clip: text;
    -webkit-background-clip: text;
    -webkit-text-fill-color: var(--shimmer-text-fill, transparent);
    animation: tw-shimmer var(--shimmer-duration, 2s) linear infinite;

    @variant dark {
        --_highlight: var(
            --shimmer-color,
            oklch(
                from currentColor max(0.8, calc(l + 0.4)) c h /
                    calc(alpha + 0.4)
            )
        );
    }

    &:where([dir="rtl"], [dir="rtl"] *) {
        animation-direction: reverse;
    }
}

@utility shimmer-once {
    animation-iteration-count: 1;
}

@utility shimmer-reverse {
    animation-direction: reverse;
}

@utility shimmer-none {
    --shimmer-image: none;
    --shimmer-text-fill: currentColor;
}

@utility shimmer-color-* {
    --shimmer-color: --value(--color, [color]);
    --shimmer-color: color-mix(
        in oklch,
        --value(--color, [color]) calc(--modifier(integer) * 1%),
        transparent
    );
}

@utility shimmer-duration-* {
    --shimmer-duration: calc(--value(integer) * 1ms);
}

@utility shimmer-spread-* {
    --shimmer-spread: calc(var(--spacing) * --value(integer));
    --shimmer-spread: --value([length], [percentage]);
}

@utility shimmer-angle-* {
    --shimmer-angle: calc(--value(integer) * 1deg);
}

@media (prefers-reduced-motion: reduce) {
    .shimmer {
        animation: none;
        background-image: none;
        -webkit-text-fill-color: currentColor;
    }
}

Usage

Add shimmer to a text element.

rx.el.p("Generating response", class_name="shimmer text-muted-foreground w-fit")

The effect is pure CSS. The text is painted with background-clip: text, and the highlight sweeps across it in a seamless loop.

Note: If the shimmer utility isn't working properly, try adding w-fit to the text styling, as it ensures the animation doesn't exceed the inherit width of the text.

Color

Use shimmer-color-<color> to set the highlight color explicitly. It accepts theme colors with an optional opacity modifier, or any arbitrary color value.

import reflex as rx


def shimmer_color():
    return rx.el.div(
        rx.el.p(
            "Generating response", class_name="shimmer shimmer-color-blue-500/60 w-fit"
        ),
        rx.el.p(
            "Generating response", class_name="shimmer shimmer-color-[#378ADD] w-fit"
        ),
        class_name="flex flex-col items-center gap-2 text-sm text-muted-foreground",
    )

Duration

Use shimmer-duration-<number> to set the duration of one sweep in milliseconds. The default is 2000, i.e. 2s.

import reflex as rx


def shimmer_duration():
    return rx.el.div(
        rx.el.div(
            rx.el.p("Generating response...", class_name="shimmer"),
            rx.el.p("shimmer", class_name="font-mono text-xs"),
            class_name="flex flex-col gap-3",
        ),
        rx.el.div(
            rx.el.p(
                "Generating response...", class_name="shimmer shimmer-duration-1000"
            ),
            rx.el.p("shimmer-duration-1000", class_name="font-mono text-xs"),
            class_name="flex flex-col gap-3",
        ),
        class_name="mx-auto grid w-full max-w-lg gap-6 text-center text-sm text-muted-foreground sm:grid-cols-2",
    )

Spread

Use shimmer-spread-<number> to set the width of the highlight band using the spacing scale. The default is calc(3ch + 40px): a fixed base plus a 3ch term that scales with the font size.

import reflex as rx


def shimmer_spread():
    return rx.el.div(
        rx.el.div(
            rx.el.p("Generating response...", class_name="shimmer shimmer-spread-4"),
            rx.el.p("shimmer-spread-4", class_name="font-mono text-xs"),
            class_name="flex flex-col gap-3",
        ),
        rx.el.div(
            rx.el.p("Generating response...", class_name="shimmer shimmer-spread-24"),
            rx.el.p("shimmer-spread-24", class_name="font-mono text-xs"),
            class_name="flex flex-col gap-3",
        ),
        class_name="mx-auto grid w-full max-w-lg gap-6 text-center text-sm text-muted-foreground sm:grid-cols-2",
    )

Angle

Use shimmer-angle-<number> to set the tilt of the highlight band in degrees. The default is 20.

import reflex as rx


def shimmer_angle():
    return rx.el.div(
        rx.el.div(
            rx.el.p("Generating response...", class_name="shimmer"),
            rx.el.p("shimmer", class_name="font-mono text-xs"),
            class_name="flex flex-col gap-3",
        ),
        rx.el.div(
            rx.el.p("Generating response...", class_name="shimmer shimmer-angle-45"),
            rx.el.p("shimmer-angle-45", class_name="font-mono text-xs"),
            class_name="flex flex-col gap-3",
        ),
        class_name="mx-auto grid w-full max-w-lg gap-6 text-center text-sm text-muted-foreground sm:grid-cols-2",
    )

Reverse

Use shimmer-reverse to sweep the highlight in the opposite direction.

import reflex as rx


def shimmer_reverse():
    return rx.el.div(
        rx.el.div(
            rx.el.p("Generating response...", class_name="shimmer shimmer-reverse"),
            rx.el.p("shimmer reverse", class_name="font-mono text-xs"),
            class_name="flex flex-col gap-3",
        ),
        class_name="flex text-center items-center gap-2 text-sm text-muted-foreground",
    )

Play Once

Use shimmer-once to play a single sweep instead of looping, useful as a reveal when streaming completes. Pair it with shimmer-duration-<number> to control how long the sweep takes.

import reflex as rx
from reflex.experimental import ClientStateVar

from components.ui.button import button

shimmer_key = ClientStateVar.create("shimmer_key", 0)


def shimmer_once():
    return rx.el.div(
        rx.el.div(
            rx.el.p(
                "Generating response...",
                class_name=(
                    "shimmer text-sm text-muted-foreground "
                    "shimmer-duration-1100 shimmer-once"
                ),
            ),
            key=shimmer_key.value.to(str),
        ),
        button(
            "Replay",
            variant="outline",
            size="sm",
            on_click=shimmer_key.set_value(shimmer_key.value.to(int) + 1),
        ),
        class_name="flex flex-col items-center gap-4",
    )

rx.el.p("Response Generated", class_name="shimmer shimmer-duration-1100 shimmer-once")

Disabling the Shimmer

Use shimmer-none to turn the effect off and render the text normally. It works in any class order, so the typical use is responsive or stateful.

import reflex as rx


def shimmer_none():
    return rx.el.div(
        rx.el.p("Generating response...", class_name="shimmer md:shimmer-none"),
        rx.el.p("shimmer md:shimmer-none", class_name="font-mono text-xs"),
        class_name="flex flex-col items-center gap-3 text-sm text-muted-foreground",
    )