For this point you need to set border-radius:50%;
so you your button will change shape to circle then add min-width:0; min-height:0;
and text-align:center;
here is the full css :
.normal-size-icon {
font-size: 24px;
font-family: 'Segoe UI Symbol';
color: rgb(555, 255, 255);
min-width: 0;
min-height: 0;
border-radius: 50%;
border-style: solid;
padding: 0;
text-align: center;
}
if you don't need border you can set border:none;
. Sorry for my bad english