if the reason is you dont like how the landing page looks on mobile may be we should start there if you can explain what you wish to change.
If I had to guess, I would replace your current rule
.page-id-880 #wrapper {width: 30%;
background: rgb(38, 38, 37); /* Fallback */
background: rgba(38, 38, 37, 0.7);
position: fixed;
top: 40%;
left: 50%;
transform: translate(-50%, -50%);}
by
.page-id-880 #wrapper {max-width: 400px;
background: rgb(38, 38, 37) !important; /* Fallback */
background: rgba(38, 38, 37, 0.7) !important;
margin-top: 20%;}
But if you simply explain what you would want the behavior to be, we can do that.
We can also change the style completely using media rules on phone and small tablets.
Just tell us what you wish to see