semi-design/packages/semi-foundation/button/splitButtonGroup.scss

$dropdown: #{$prefix}-dropdown;
$module: #{$prefix}-button;
$component: #{$module}-split;
$content: #{$module};
$icon: #{$module}-with-icon;

.#{$component} {
    display: inline-block;

    .#{$module} {
        border-radius: 0;
        margin-right: 1px;
    }

    :first-child {
        border-top-left-radius: var(--semi-border-radius-small);
        border-bottom-left-radius: var(--semi-border-radius-small);
    }

    :last-child {
        border-top-right-radius: var(--semi-border-radius-small);
        border-bottom-right-radius: var(--semi-border-radius-small);
        margin-right: unset;
    }

    &:hover {
        // 因为上面那条规则，导致原来的active被覆盖
        .#{$module}-borderless:active {
            background-color: $color-button_borderless-bg-active;
        }
    }
}