.knopka:focus{
color: yellow;
}
<label class="button">
<input type="radio" name="button">
<span>click me</span>
</label>
<label class="button">
<input type="radio" name="button">
<span>click me</span>
</label>.button input {
display: none;
}
.button input:checked + span {
background: red;
color: white;
}
