<!--1. button with a text -->
<button type="button" class="btn btn-success" id="newWord">Save</button>
<!--2. button only with a close icon -->
<button type="button" class="close"></button>
<!--3. button is a link -->
<a class="btn btn-success btn-xs" href="#">Save</a>
button,
button:active,
button:focus,
button:hover,
.btn,
.btn:active,
.btn:focus,
.btn:hover{
outline:none !important;
}
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
<!-- this button has default style -->
<button>Action</button>
<!-- this button is clear of style -->
<button class="btn-clear">Action</button>
<label id="action"></label>
更新 : docs link for bootstrap 5: https://getbootstrap.com/docs/5.1/utilities/shadows/,and for beta: < a href = “ https://getbootstrap.com/docs/5.2/tools/shadow/”rel = “ noReferrer”> https://getbootstrap.com/docs/5.2/utilities/shadows/