[css] Bootstrap Responsive Text Size

I am trying to build a responsive layout using bootstrap and currently am defining some of the titles with font-size:3em;

But when the layout is shrunk down this is too big. How can I responsively reduce the size of the text?

Well, my solution is sort of hack, but it works and I am using it.

1vw = 1% of viewport width

1vh = 1% of viewport height

1vmin = 1vw or 1vh, whichever is smaller

1vmax = 1vw or 1vh, whichever is larger

h1 {
  font-size: 5.9vw;
}
h2 {
  font-size: 3.0vh;
}
p {
  font-size: 2vmin;
}