@mixin box($bg_color: white, $border_color: black) {
    border-radius: 10px;
    padding: 10px;
    border: 1px solid $border_color;
    background-color: $bg_color;
    color: $page_text_color;
}
@mixin error_box {
    @include box($error_box_color, $error_box_border_color);
}
@mixin info_box {
    @include box($info_box_color, $info_box_border_color);
}
@mixin success_box {
    @include box($success_box_color, $success_box_border_color);
}
@mixin warning_box {
    @include box($warning_box_color, $warning_box_border_color);
}

@mixin button {
    display: block;
    text-decoration: none;
    text-align: center;
    font-size: 100%;

    @include box(lighten($header_border_color, 40%), $header_border_color);

    &:hover {
        background-color: lighten($header_border_color, 30%);
    }
    &:focus {
        background-color: lighten($header_border_color, 20%);
        box-shadow: 0 0 1.5px 1px $header_bg_color;
    }
}