XF 2.0 Where are the style properties for the blockMessage errors?

[HUHjdfhafuIIIY]

I'm looking to customize the color of URLs that appear in the block messages on the login page.

I've customized my login page with a link to a page where people can go to join the group:

<xf:js src="xf/login_signup.js" min="1" />

<xf:title>{{ phrase('log_in') }}</xf:title>
<div class="blockMessage">
    You must be a member to view the forum. Not a member? <a href="https://mysite.com/store/products/membership/">Join the waitlist.</a>
</div>
<xf:if contentcheck="true">
    <div class="blockMessage blockMessage--error blockMessage--iconic">
        <xf:contentcheck>{$error}</xf:contentcheck>
    </div>
</xf:if>

I can add custom CSS if necessary, but I'm wondering if there's a setting somewhere that controls the styling of messages in the blockMessage divs.