ionic-framework/ionic/components/button/extensions/material.scss

// Material Design Button
// --------------------------------------------------

$button-material-font-size:                1.4rem !default;
$button-material-min-height:               3.6rem !default;
$button-material-padding:                  0 1.6rem !default;
$button-material-box-shadow:               0 1px 1.5px 0 rgba(0, 0, 0, 0.12),0 1px 1px 0 rgba(0, 0, 0, 0.24);//0 1px 3px 0 rgba(0, 0, 0, 0.3); //0 2px 5px 0 rgba(0, 0, 0, 0.26) !default;
$button-material-box-shadow-active:        0 4px 5px 0 rgba(0, 0, 0, 0.14),0 1px 10px 0 rgba(0, 0, 0, 0.12),0 2px 4px -1px rgba(0, 0, 0, 0.2); //0 1px 3px 0 rgba(0, 0, 0, 0.3); //0 2px 5px 0 rgba(0, 0, 0, 0.26) !default;
$button-material-border-radius:            3px !default;


[mode="md"] button,
[mode="md"] [button] {
  border: 0;
  border-radius: $button-material-border-radius;

  min-height: $button-material-min-height;

  padding: $button-material-padding;
  text-transform: uppercase;

  font-weight: 500;
  font-size: $button-material-font-size;
  box-shadow: $button-material-box-shadow;

  transition: box-shadow 0.2s $animation-curve-fast-out-linear-in,
              background-color 0.2s $animation-curve-default,
              color 0.2s $animation-curve-default;

  &.activated {
    box-shadow: $button-material-box-shadow-active;
  }

  &[icon] {
    font-size: $button-icon-size;
  }

  &[large][icon] {
    font-size: $button-large-icon-size;
  }

  &[small][icon] {
    font-size: $button-small-icon-size;
  }

  &[outline] {
    box-shadow: none;

    .md-ripple {
      &.is-visible {
        opacity: 0.2;
      }
    }
  }

  &[fab] {
    border-radius: 50%;
  }

  @each $color, $value in $colors {

    &[#{$color}] {

      @if lightness(get-color($color, base)) < 80 {
        .md-ripple {
          background-color: white;
        }
      }

      &.activated {
        opacity: 1;
        background-color: get-color($color, base);
      }

      &[outline] {
        @if lightness(get-color($color, base)) >= 80 {
          .md-ripple {
            background-color: black;
          }
        } @else {
          .md-ripple {
            background-color: get-color($color, base);
          }
        }

        &.activated {
          opacity: 1;
          background: transparent;
        }
      }

      &[clear] {
        box-shadow: none;

/*        @if lightness(get-color($color, base)) > 90 {
          color: get-color($color, inverse);
        }*/

        &:hover,
        &.hover {
          background-color: rgba(158, 158, 158, 0.2);
        }
        &:activated {
          background-color: rgba(158, 158, 158, 0.4);
        }
      }
    }
  }
}