Customize the Devise `unlock_instructions` email

app/views/devise/mailer/unlock_instructions.html.haml

-%p
-Hello #{@resource.name}!
-
-%p
+.center
+  #content
+    %h2 Hello, #{@resource.name}!
+    %p
       Your GitLab account has been locked due to an excessive amount of unsuccessful
-  sign in attempts. Your account will automatically unlock in
-  = time_ago_in_words(Devise.unlock_in.from_now)
+      sign in attempts. Your account will automatically unlock in #{time_ago_in_words(Devise.unlock_in.from_now)}
       or you may click the link below to unlock now.
-
-%p= link_to 'Unlock your account', unlock_url(@resource, unlock_token: @token)
+    #cta
+      = link_to('Unlock account', unlock_url(@resource, unlock_token: @token))

app/views/devise/mailer/unlock_instructions.text.erb

+Hello, <%= @resource.name %>!
+
+Your GitLab account has been locked due to an excessive amount of unsuccessful
+sign in attempts. Your account will automatically unlock in <%= time_ago_in_words(Devise.unlock_in.from_now) %>
+or you may click the link below to unlock now.
+
+<%= unlock_url(@resource, unlock_token: @token) %>