Allow custom themes + dark theme

[GammaGames]

I use the AdminerCustomizeThemeBasedOnServer plugin to add custom css to the header depending on the server the user is connected to:

@keyframes blinker {
    50% {
        opacity: 10%;
    }
}

a#h1:after, #content h2:nth-of-type(1)::after {
    content: ' DEV SERVER';
    color: red;
    animation: blinker 2s linear infinite;
    font-weight: bold;
}

If this plugin finds a matching css file adminer's dark theme no longer works, I think because of

adminer/adminer/include/design.inc.php

Line 34 in 9cfea02

$dark = (count($css) == 1 ? !!preg_match('~-dark~', $css[0]) : null);

Could adminer be updated to allow extra custom css on top of the dark theme?

[vrana]

I'll make it explicitly check for adminer.css and adminer-dark.css.