You may wanna try this code:
The script will target the sign in button by its inner text, so you if your button have a different text, please update line 9 in the script.

<script>
document.addEventListener("DOMContentLoaded", function () {
function addMessage() {
const userAccountsDiv = document.querySelector("#your-block-name");
if (!userAccountsDiv) return setTimeout(addMessage, 1000);
const signupButton = [...userAccountsDiv.querySelectorAll("button")]
.find(btn => btn.textContent.trim() === "Sign In");
if (!signupButton) return setTimeout(addMessage, 1000);
if (!document.querySelector("#terms-message")) {
const message = document.createElement("p");
message.id = "terms-message";
message.innerHTML = `By signing in, you agree to our
<a href='#' class='terms-link'>User Agreement</a> &
<a href='#' class='terms-link'>Privacy Policy</a>.`;
Object.assign(message.style, {
fontSize: "12px",
color: "#666",
marginTop: "10px",
whiteSpace: "nowrap" // Prevent text wrapping
});
signupButton.parentNode.insertBefore(message, signupButton.nextSibling);
message.querySelectorAll("a").forEach(link =>
Object.assign(link.style, {
color: "#007bff",
textDecoration: "none",
display: "inline" // Ensures links stay inline
})
);
}
}
addMessage();
});
</script>