I have a webpage HTML & JS.
I need to add a red waved-line under misspelled words. I got my algorithm to detect those words but I just need to know how put a waved line under those words.
Actually you don't have a standard curly underline just by using CSS, but check this tutorial on how to create one yourself:
Taken from here: http://www.phpied.com/curly-underline/
.curly-underline {
background: url(underline.gif) bottom repeat-x;
}