select2/docs/_sass/_dl-panels.scss

.s2-docs-panels {
    dt, dd {
        border: 1px solid $panel-default-border;
    }

    dt {
        background-color: $panel-default-heading-bg;
        border-top-left-radius: $panel-border-radius;
        border-top-right-radius: $panel-border-radius;
        padding: 5px 7.5px;
    }

    dd {
        background-color: $panel-bg;
        border-bottom-left-radius: $panel-border-radius;
        border-bottom-right-radius: $panel-border-radius;
        margin-bottom: 0.75em;
        padding: 7.5px;
    }

    dt + dd {
        border-top: none;
    }
}