I have a website, backend using Django, frontend using normal HTML5.

I want to change all the default selection box to the class: "selectpicker" once in some place so it could be implemented in all the selection box in the websites.

How could I do that in one place?

I have tried:

base.html

<style>
select {
class="selectpicker";
}
</style>
    ...

app.html

    {% extends 'base.html' %}
<style>
select {
class="selectpicker";
}
</style>

But failed to do so.

I want this kind of solution, better only make change in base.html to change all the selection box in the websites as I have tons of HTML in my website.