We need to move the div present inside button from that button inside to button's out side meaning
<div class="Content__Btn-Container">
<button class="Btn Btn-Small ">
<span class="Btn__Title Btn--Block Btn-Slash "></span>
<svg class="svg-inline--fa fa-sort-down fa-w-10 Btn__Arrow" aria-hidden="true" focusable="false" data-prefix="fas" data-icon="sort-down" role="img" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 320 512" data-fa-i2svg=""><path fill="currentColor" d="M41 288h238c21.4 0 32.1 25.9 17 41L177 448c-9.4 9.4-24.6 9.4-33.9 0L24 329c-15.1-15.1-4.4-41 17-41z"></path>
</svg>
</button>
<div class="Btn-Collection ">
<button class="Btn Btn-DropDown "><span class="Btn__Title Btn--Block ">Inches</span></button>
<button class="Btn Btn-DropDown "><span class="Btn__Title Btn--Block ">Matric</span></button>
</div>
</div>