Can I keep "unused css selector"?

I noticed that svelte will purge my css automatically, all "unused css selector" will get removed.

For example:

<p class="blue">This is a paragraph.</p><style>    .red{        color: red;    }    .blue{        color: blue;    }</style>

The style for class 'red' will be removed. How can I keep the '.blue' selector? I want to use it later at some point.