Can't change textbox (text input) width

I'm using Twine 2, Sugarcube 2.

I have a passage where I use <<textbox, and I'm trying to change the width (make it narrower).

This is the CSS I'm using:

input, input:focus, input:hover {background-color: #000;
color: #f0f0f0;
font-family: Helvetica, sans-serif;
font-size: 100%;
border: 1px solid #f0f0f0;
min-width: 8em;
max-width: 8em;
width: 8em;}

But this only changes the width for when I'm hovering on the text box, or clicking inside it. Its default (no focus, no hover) size, however, remains the same.

What can I do?