Tw-icon opacity not responding CSS - visibility undo button

Twine Version: 2.3.13
Story Format: Harlowe 3.2.1

Hi there, I used this code: How do I replace or style the Back and Forward buttons? - Twine Forum, but the opacity command does not change anything. It’s weird, because if I change color for example in tw-icon, it does work.
My full CSS code looks like this:

tw-link {
.enchantment-link:hover, tw-link:hover {
tw-passage {
text-align: center;
font-size: 2.5vh;
font-size: 2.5vw;
font-size: 2.5vmin;
line-height: normal;
position: relative;

.transition-in[data-t8n^=dissolve] {
-webkit-animation:appear 0ms step-start;
animation:appear 0ms step-start
.enchantment-mouseover {
border-bottom: hidden;
tw-story {
margin-top: 0;
opacity: 1.0;
color: white;
tw-icon:hover {
opacity: 0.1;
font-weight: bold;

Could anyone help me out? I’d like my undo (and redo) button be more visible.
Thank you in advance, cheers!

Never mind, I found the answer by looking at the HTML output.
The answer is:
tw-icon[alt] {
opacity: 1.0;