[jgneff]

I doubt e-readers have support for SVG filters, but the following added to your SVG file works pretty well in most browsers for general dark-mode support. Just add it right after the opening svg element.

<filter id="darkmode">
    <!-- Same as CSS 'filter: invert(1)' but in linear RGB -->
    <feComponentTransfer>
        <feFuncR type="table" tableValues="1 0"/>
        <feFuncG type="table" tableValues="1 0"/>
        <feFuncB type="table" tableValues="1 0"/>
    </feComponentTransfer>
    <!-- Same as CSS 'filter: hue-rotate(180deg)' -->
    <feColorMatrix type="hueRotate" values="180"/>
    <!-- Gamma function: C' = amplitude * pow(C, exponent) + offset -->
    <feComponentTransfer>
        <feFuncR type="gamma" exponent="2.2"/>
        <feFuncG type="gamma" exponent="2.2"/>
        <feFuncB type="gamma" exponent="2.2"/>
    </feComponentTransfer>
</filter>
<style>
@media (prefers-color-scheme: dark) {
    svg {filter: url('#darkmode');}
}
</style>

It inverts the colors (really just to go from light to dark), swings back around 180 degrees to the original color hues, and then converts the gamma back to sRGB from linear RGB. You can try changing or removing the gamma function if it's too dark even for dark mode.