For the sentence about the web page:
Both showing and with sound perfectly fine to me, the first one probably being the most idiomatic. I am not sure whether of would be correct in this case, but I cannot recall having seen that preposition being used before in this context. Now, the word containing also sounds odd. Let's have a look at its definition first:
to have something inside or include something as a part (source)
Search results are shown on a page, not in a page and rather than being "a part" of the page, the search results are really what the page is all about so contain does not really seem the right verb to use.
I think showing is your best option here.
For the sentence about the HTML-tag:
Again, with seems to be fine here and as opposed to the other sentence, I think containing can perfectly be used as well. In HTML, as you probably know, the text for an element are placed within its tags, meaning that the text is inside the HTML element, so the definition of contain fits perfectly. Allow me to illustrate with an example:
The text is contained within the
<span> tags here.
Now, about labeled with: I wouldn't use this phrase here. It could cause confusion since it could be interpreted as not actually having the text within the HTML element, but rather having it in the
title attribute or the
data-label or similar attributes:
<span title="StackExchange">Not SE</span>
<span data-label="StackExchange">Not SE</span>
To describe the search results on a web page, showing is probably the way to go. To describe the text within an HTML element, you can definitely use containing. In both cases, with seems to be working fine as well.