It depends in many things… You are using a theme that overrides the default theme and now you overrides some styles of the theme you install.
First, you need to see in developer tools how the element is identified. Because you need to override what is ‘injected’ by the “Shimmering” theme.
This to say it’s not a simple answer!
I installed the theme and identified this (green is the color defined by the theme for normal highlight):
On the right, in styles, you see this code:
.markdown-preview-view mark, .cm-s-obsidian span.cm-highlight {
background-color: var(--highlight-color);
}
This is what you need to change. But, in a simple way, you just need to go to the css file of the theme and check in “root” and “theme-light” and “theme-dark” the names and values of this “–highlight-color”. Then, use the same names and change the colors.
Well, this is the “logic” way… But is not possible in the way the theme define the “–highlight-color” versus want you want. Because is a single color without variations in dark/light modes: it’s the same in both.
So, in short answer (sorry for my illogic and confused answer), using what you already defined, try this:
.markdown-preview-view mark, .cm-s-obsidian span.cm-highlight {
background-color: var(--highlight-yellow);
}