方法
①擬似要素の利用
<ul class="list_nav_header">
<li><a href="#">ABOUT.</a></li>
<li><a href="#">FEATURE.</a></li>
<li><a href="#">PROFILE.</a></li>
<li><a class="btn_ico_mail" href="#">CONTACT.</a></li>
</ul>
[class*="btn_ico"] {
display: block;
height: 36px;
display: flex;
align-items: center;
padding: 0 30px 0 60px;
font: 400 18px/1em 'futura', 'noto sans japanese', sans-serif;
background: #00CCFF;
position: relative;
}
[class*="btn_ico"]:before {
content: "";
display: block;
width: 40px;
height: 40px;
background-position: center center;
background-repeat: no-repeat;
background-size: contain;
position: absolute;
top: 50%;
left: 15px;
transform: translateY(-50%);
}
[class*="btn_ico"][class*="mail"]:before {
background: url(../img/ico/ico_mail.svg);
}