a.Button(href="#0", data-tooltip="File size: 50MB")
  span.Button__textWrapper
    span.Button__text Download
    span.Button__icon(aria-hidden="true")
View Compiled
//- BASE

*,
*:after,
*:before { box-sizing: border-box; }

html { font-size: 16px; }

body {
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 100%;
  font-family: 'PT Sans', sans-serif;
  background-color: #150811;
  height: 100vh;
}

a { text-decoration: none; }

//- COMPONENT
$duration: 500ms;
$button-height: 60px;
$button-width: 200px;
$tooltip-height: 60px;
$tooltip-width: 140px;

%Button__element {
  position: absolute;
  width: 100%;
  height: 100%;
  left: 0;
}

%Button__transitionable {
  transition: top $duration;
}

.Button {
  display: inline-block;
  position: relative;
  background-color: #0CBABA;
  color: #fff;
  font-size: 1.2rem;
  border-radius: 1000px;
  width: $button-width;
  height: $button-height;
  box-shadow: 0 2px 20px rgba(#000, 0.7), inset 0 1px rgba(#fff, 0.3);
  text-align: center;
  transition: background-color $duration, transform 100ms;
  
  &__textWrapper {
    @extend %Button__element;
    overflow: hidden;
  }
  
  &__text {
    @extend %Button__element;
    @extend %Button__transitionable;
    line-height: $button-height;
    top: 0;
  }
  
  &__icon {
    @extend %Button__element;
    @extend %Button__transitionable;
    top: 100%;
    background: url('https://cl.ly/0X3o100h2H0g/icon-download.svg') no-repeat center center;
  }
  
  // Tooltip
  &::before {
    content: attr(data-tooltip);
    width: $tooltip-width;
    height: $tooltip-height;
    background-color: #EEB868;
    font-size: 1rem;
    border-radius: .25em;
    line-height: $tooltip-height;
    bottom: 90px;
    left: calc(50% - 70px);
  }
  
  &::after {
    content: '';
    width: 0;
    height: 0;
    border: 10px solid transparent;
    border-top-color: #EEB868;
    left: calc(50% - 10px);
    bottom: 70px;
  }
  
  &::before,
  &::after {
    position: absolute;
    opacity: 0;
    transition: all $duration;
    visibility: hidden;
  }
  
  //- button hover
  &:hover {
    background-color: #01BAEF;
    
    .Button__text { top: -100%; }
    
    .Button__icon { top: 0; }
    
    &::before,
    &::after {
      opacity: 1;
      visibility: visible;
    }
    
    &::after { bottom: 60px; }
    
    &::before { bottom: 80px; }
  }
  
  &:active { transform: translate(2px, 2px); }
}
View Compiled
Run Pen

External CSS

  1. https://fonts.googleapis.com/css?family=PT+Sans

External JavaScript

This Pen doesn't use any external JavaScript resources.