The code for the search form itself can be edited in your pM Control Panel: Edit Templates > search > Search Form Templates. If you look at the code, there is no specific style applied to that text. It will, however, inherit any styles you might have applied to parent elements.
Anyway, if you wanted to style that text specifically, you could wrap it in a span:
<span class="separateKeywords">Separate keywords with spaces</span>
Then add the style to your stylesheet (you could add it to “search.css” or “meislik.css” since both are used on that page) using whatever styles you want:
.separateKeywords {
font-size: 0.8em;
}
> can we have more than one CSS stylesheet per page
Yes, you can reference multiple stylesheets. If more than one of them contains the same style information (i.e., if both had the “separateKeywords” class) then the last stylesheet referenced takes priority.