When customizing the default theme, adding new CSS properties causes these to "leak" through to other themes when their properties aren't set. This is because the default theme is persistent, and always loads regardless of which theme is selected.

Header styling from default theme leaking through to "Deep" theme.
I found a solution by adding "disabled" to the default CSS theme when changing themes, and removing it when switching back to each html file under themes. But I don't know if it's good code. (I only know some HTML/CSS)
<link rel="stylesheet" href="<% echo(skindir) %>css/mono_main.css?v=1.1" id="css0">
<link rel="stylesheet" href="<% echo(skindir) %>css/mono_dev.css" id="css1" disabled>
<link rel="stylesheet" href="<% echo(skindir) %>css/mono_dark.css" id="css2" disabled>
<link rel="stylesheet" href="<% echo(skindir) %>css/mono_deep.css" id="css3" disabled>
<link rel="stylesheet" href="<% echo(skindir) %>css/mono_mayo.css" id="css4" disabled>
<script>
var colorIdx = GetCookie("colorIdx");
switch (Number(colorIdx)) {
case 0:
document.getElementById("css0").removeAttribute("disabled");
break;
case 1:
document.getElementById("css1").removeAttribute("disabled");
document.getElementById("css0").setAttribute("disabled", "");
break;
case 2:
document.getElementById("css2").removeAttribute("disabled");
document.getElementById("css0").setAttribute("disabled", "");
break;
case 3:
document.getElementById("css3").removeAttribute("disabled");
document.getElementById("css0").setAttribute("disabled", "");
break;
case 4:
document.getElementById("css4").removeAttribute("disabled");
document.getElementById("css0").setAttribute("disabled", "");
break;
}
When customizing the default theme, adding new CSS properties causes these to "leak" through to other themes when their properties aren't set. This is because the default theme is persistent, and always loads regardless of which theme is selected.

Header styling from default theme leaking through to "Deep" theme.I found a solution by adding "disabled" to the default CSS theme when changing themes, and removing it when switching back to each html file under themes. But I don't know if it's good code. (I only know some HTML/CSS)