<div class="form-left__sex">
<label for="">Пол:</label>
<input type="radio" id="man" name="sex" checked> мужчина
<input type="radio" id="wooman" name="sex"> женщина
</div>
.form form .form-left__sex input:checked::before {
content: url(../img/icons/radio-active.png);
position: relative
}
.form form .form-left__sex input::before {
content: url(../img/icons/radio.png);
left: -20px;
position: relative;
top: 1px
}
<input>
<span></span>
input:checked + span {}
input:checked ~ span {}
display:none;
)