bbPress.org

in your css you have

img {
height: 28px;
min-width: 0;
width: 175px;
}

which is determining this display

Not sure where it is set in your theme, I see the resultant output in a browser inspector.

If you theme has a custom css area, then put the above in there and play with the settings

If you don’t then there are several custom css plugins (google) or my style pack plugin has a custom css tab

bbp style pack

you may need to put !important after a setting to get it to take eg

img {
height: 28px;
min-width: 0;
width: 100px !important;
}