HTML's <del>...</del> and <ins>...</ins> are included for use as editorial "laymarks".
I have never used either of them.
There's also a very old, now deprecated, tag <s>...</s> for strikethrough.
Whilst <del> generally results in a single strikethrough, W3C leaves it open as to how <del> (and <ins>) markup should be rendered. The HTML 4.01 Recommendation says that, "User agents should render inserted and deleted text in ways that make the change obvious. For instance, inserted text may appear in a special font, deleted text may not be shown at all or be shown as struck-through or with special markings, etc."
As far as I know, no CSS directive will successfully override any browser's rendering of strikethough achieved with either <del> or <s>, though you can add further style directives such as italics, bold, background-color or whatever.
I recall once seeing a suggestion that using a background image was the only way to achieve double strikethrough, as Stbuchok has already said.