app/views/user_mailer/send_verify_code.html.erb
<h2 style="font-weight: 400; color: #323232;">您的邮箱校验码是</h2>
<div style="background-color: #C5EDFE; color: #0983B6; display: inline-block; padding: 10px 30px; font-size: 23px; font-weight: bold; letter-spacing: 5px; border: 1px solid #b5e0f3; border-radius: 2px;">
<span style="display: inline-block; margin-right: 8px;"><%= @code[0..2] %></span><span style="display: inline-block;"><%= @code[3..-1] %></span>
</div>
<p style="color: #888; font-size: 15px; margin-top: 30px; letter-spacing: 0.5px; font-weight: 200;">
该校验码30分钟内有效，请勿泄露给他人。<br />
如非本人操作，请忽略此邮件。
</p>