Yes, but &quot;alert&quot; simply means &quot;this is an alert&quot; (so, it may be a box or a popup, depending on where it is on the app&#x2F;website). &quot;alert alert-danger&quot; means that this alert, whatever shape it is in, is also the alert for danger. It may be red, yellow, blink, have javascript attached to it, etc.<p>However, it is not &quot;alert alert-red&quot;... What if your client wanted to never use the colour red again because his competition is branded red? You need to go through all the CSS (a few lines of :red needs to be changed to :yellow). You however also need to go through all your view, templates, possibly some hardcoded parts of the code, to change &quot;alert-red&quot; to &quot;alert-yellow&quot;... simply have it &quot;alert-danger&quot;.