.btn {
    background: linear-gradient(to bottom, #f2f2f9 21%,#CDD1D9 80%);
    border:1px solid $color-border-input;
    border-radius:.4em;
    box-sizing: content-box;
    color: $color-heading-2;
    display:inline-block;
    line-height: 1em;
    padding: .5em 1em;
    font-size: (14rem/16);
    font-weight:normal;
    vertical-align: middle;

    &:hover {
    background: linear-gradient(to bottom, #f8f8fd 21%, #d5dfe4 80%);
    cursor: pointer;
    text-decoration: none;
    }
    &-action {
        @extend .btn;
    }
    &-featuredAction {
        @extend .btn-action;
        font-size: (24rem/16);
    }
    &-container {
            @include clearfix();
            margin: 1em 0;
        &--centered {
            @extend .btn-container;
            text-align: center;
        }
        > [class^=btn] {
            margin: 0 1em 0 0;
        }
    }
}

.btn {
    background: $color-table-background;
    border:1px solid $color-border-input;
    border-radius:.4em;
    box-sizing: content-box;
    color: $color-heading-2;
    display:inline-block;
    line-height: 1em;
    padding: .5em 1em;
    font-size: (14rem/16);
    font-weight:normal;
    vertical-align: middle;

    &:hover {
    background: lighten($color-table-background, 1);
    cursor: pointer;
    text-decoration: none;
    }
    &-action {
        @extend .btn;
    }
    &-featuredAction {
        @extend .btn-action;
        font-size: (24rem/16);
    }
    &-container {
            @include clearfix();
            margin: 1em 0;
        &--centered {
            @extend .btn-container;
            text-align: center;
        }
        > [class^=btn] {
            margin: 0 1em 0 0;
        }
    }
}

Replace button gradient with flat background color in default.
Replace button gradient with flat background color in default.

The gradient background proved to be a hassle to override in all of the themes that built on top of default. Theme authorship is more manageable if buttons use a flat background color instead. Theme authors can specify a gradient in their themes, if they would like.