ds-site/Resources/Private/Sass/Frontend/components/_admonition.scss

aside {
    &[class^='admonition-'] {
        border: none;
        border-left: solid calc($spacer / 4);
        padding: calc($spacer * 2);
        margin-top: calc($spacer * 2);

        h1, h2, h3, h4, h5, h6 {
            padding-top: 0;
            letter-spacing: 1em;
        }
    }

    &.admonition-note {
        border-color: $yellow;
    }

    &.admonition-task,
    &.admonition-hint {
        border-color: $green;
    }

    &.admonition-caution {
        border-color: $red-dark;
    }

    &.admonition-danger {
        border-color: $red-dark;
    }
}