[Bug] The Submit button does not display properly

[NoverNobida]

Describe the bug
On the mobilebrowser, this button will overwrite the menu like this.

Maybe

.input-group-prepend .btn {
 position:relative;
 z-index:2
}

should be

.input-group-prepend .btn {
 position:relative;
 z-index:auto
}

Screenshots