How can I make padding not move other elements down?

I am trying to make a row of three buttons. One of the buttons has a :hover property that makes its margin-top increase. This looks something like this:

button {
  position: relative;
  height: 45px;
  width: 150px;
  margin: 10px 8px;
  padding: 5px 5px;
  font-weight: 700;
  font-size: 15px;
  letter-spacing: 2px;
  color: #383736;
  border: 2px #383736 solid;
  border-radius: 4px;
  text-transform: uppercase;
  outline: 0;
  overflow:hidden;
  background: none;
  z-index: 1;
  cursor: pointer;
  transition: 0.15s;
}

button:hover {
  color: whitesmoke;
}

.btn:hover:before {
  right: 0;
}

.btn:before {
  content: "";
  position: absolute;
  background: #383736;
  bottom: 0;
  left: 0;
  right: 100%;
  top: 0;
  z-index: -1;
  transition: right .15s;
}

.btn2:hover:before {
  top: 0;
}

.btn2:before {
  content: "";
  position: absolute;
  background: #383736;
  bottom: 0;
  left: 0;
  top: 100%;
  right: 0;
  z-index: -1;
  transition: top .15s;
}

.continue {
  border-color: lime;
  color: lime;
}

.continue:before {
  content: "";
  background-color: lime;
}

.continue:hover {
  padding-top: 20px;
}

.continue:hover:before {
  content: "\2192";
}

<button class = "btn">
  HOVER
</button>

<button class = "btn2">
  HOVER
</button>

<button class = "btn continue">
  CONTINUE
</button>

When you hover the third button, it's padding-top changes and therefore the other two buttons move down. What can I do to make it so that this has the same effect, except the other two buttons don't move?