BookStack/resources/assets/sass/_buttons.scss

button {
  background-color: transparent;
  border: 0;
  font-size: 100%;
}

.button  {
  text-decoration: none;
  font-size: 0.85rem;
  line-height: 1.4em;
  padding: $-xs*1.3 $-m;
  margin-top: $-xs;
  margin-bottom: $-xs;
  display: inline-block;
  font-weight: 400;
  outline: 0;
  border-radius: 2px;
  cursor: pointer;
  transition: background-color ease-in-out 120ms,
    filter ease-in-out 120ms,
    box-shadow ease-in-out 120ms;
  box-shadow: none;
  background-color: var(--color-primary);
  color: #FFF;
  fill: #FFF;
  text-transform: uppercase;
  border: 1px solid var(--color-primary);
  vertical-align: top;
  &:hover, &:focus, &:active {
    background-color: var(--color-primary);
    text-decoration: none;
    color: #FFFFFF;
  }
  &:hover {
    box-shadow: $bs-light;
    filter: brightness(110%);
  }
  &:focus {
    outline: 1px dotted currentColor;
    outline-offset: -$-xs;
    box-shadow: none;
    filter: brightness(90%);
  }
  &:active {
    outline: 0;
  }
}

.button.outline {
  background-color: transparent;
  color: #666;
  fill: currentColor;
  border: 1px solid #CCC;
  &:hover, &:focus, &:active {
    border: 1px solid #CCC;
    box-shadow: none;
    background-color: #F2F2F2;
    filter: none;
  }
  &:active {
    border-color: #BBB;
    background-color: #DDD;
    color: #666;
    box-shadow: inset 0 0 2px rgba(0, 0, 0, 0.1);
  }
}

.button + .button {
  margin-left: $-s;
}

.button.small {
  font-size: 0.75rem;
  padding: $-xs*1.2 $-s;
}

.text-button {
  cursor: pointer;
  background-color: transparent;
  padding: 0;
  margin: 0;
  border: none;
  user-select: none;
  font-size: 0.75rem;
  line-height: 1.4em;
  color: var(--color-primary);
  fill: var(--color-primary);
  &:active {
    outline: 0;
  }
  &:hover {
    text-decoration: none;
  }
  &:hover, &:focus {
    color: var(--color-primary);
    fill: var(--color-primary);
  }
}

.button.block {
  width: 100%;
  text-align: left;
  display: block;
}

.button.icon {
  .svg-icon {
    margin-right: 0;
  }
}

.button.svg {
  svg {
    display: inline-block;
    position: absolute;
    left: $-m;
    top: $-s - 2px;
    width: 24px;
    height: 24px;
  }
  padding: $-s $-m ($-s - 2px) ($-m*2 + 24px);
}

.button[disabled] {
  background-color: #BBB;
  cursor: default;
  border-color: #CCC;
  &:hover {
    background-color: #BBB;
    cursor: default;
    box-shadow: none;
  }
}