Bootstrap 3的btn-default类在Bootstrap 4中的等价替代类是什么？

Hey there! Let's break down your two questions clearly:

1. What's the equivalent of Bootstrap 3's btn-default in Bootstrap 4? #

Bootstrap 4 completely revamped its component color naming to be more semantic, and that included buttons. The old btn-default class — which gave you that standard gray, default-state button — was replaced with btn-secondary.

This change fits Bootstrap 4's new color system logic:

• btn-primary remains the main, high-emphasis action button
• btn-secondary takes on the role of the default, low-key secondary button (exactly what btn-default did in v3)

2. Is there an equivalent implementation for the Bootstrap 3 <a class="btn btn-default">link</a> in Bootstrap 4? #

Absolutely! You just need to swap out the btn-default class for btn-secondary. The equivalent code would be:

<a class="btn btn-secondary">link</a>

This renders a button-styled link that matches the visual purpose of your original Bootstrap 3 button: a neutral, non-primary option ideal for secondary actions or links you want to style like buttons. You might notice minor styling tweaks (like rounded corners or padding adjustments) to fit Bootstrap 4's design system, but the core appearance and role are identical to the v3 btn-default link button.

内容的提问来源于stack exchange，提问作者George_kane