我该怎么做？我尝试向右浮动，但没有成功。为什么？
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<div class="dropdown float-right">
<button class="btn btn-secondary dropdown-toggle bg-success " type="button"
id="dropdownMenuButton" data-toggle="dropdown"><i class="fas fa-user"></i></button>
<div class="dropdown-menu dropdown-menu-right" aria-labelledby="dropdownMenuButton">
<a class="dropdown-item" href="#">Profile</a>
<a class="dropdown-item" href="#">Change Password</a>
<a class="dropdown-item" href="log in.html">Log out</a>
</div>
</div>