That CSS only touches padding and background — it doesn't touch line-height, height, or display, which is why zeroing the padding didn't fix the height. Since the screenshot still shows a tall block even with padding:0px 20px,the height is coming from one of these instead:Most likely:the anchor is flex-stretched to match the menu's height. Divi 5 menus commonly render as display: flex on the / with align-items: stretch, so the  fills 100% of the parent's height regardless of its own padding. Your padding:0 shrank the text box but the element itself is still being stretched to fill its flex container.
Also likely contributing:inherited line-height. If the theme's base menu a has something like line-height:60px or line-height:1.5 on a large font-size,that alone creates height even at zero padding.
Try adding this to what you have:css
li.cta-button{display:flex;align-items:center}li.cta-button a{background-color:#82a8be;color:#fff!important;padding:8px 20px!important;line-height:normal;display:inline-block;align-self:center;margin-top:0}li.cta-button a:hover{background-color:#e64a19}