#knopka{
width: 125px;
height: 60px;
border-radius: 10px;

font-size: 24px;
 background: -moz-linear-gradient(top, #D5872A, #7F5119);
 background: -o-linear-gradient(top, #D5872A, #7F5119);
 background: -ms-linear-gradient(top, #D5872A, #7F5119);
 background: -webkit-linear-gradient(top, #D5872A, #7F5119);
}
#knopka:hover {
 background: -moz-linear-gradient(top, #D5872A, #FF0000);
 background: -o-linear-gradient(top, #D5872A, #FF0000);
 background: -ms-linear-gradient(top, #D5872A, #FF0000);
 background: -webkit-linear-gradient(top, #D5872A, #FF0000);
}