<a class="header__link-footer" href="#">Play Demo</a>
.header__link-footer {
position: relative;
font-family: 'Poppins', serif;
font-size: 17px;
color: rgb(104, 109, 119);
font-weight: 500;
padding-left: 40px;
}
.header__link-footer::after {
position: absolute;
content: '';
background-image: url(../img/src/Play\ button.svg);
background-repeat: no-repeat;
top: 80%;
left: 50%;
transform: translate(-120%, -50%);
width: 100px;
height: 100px;
}
.header__link a {
display: flex;
align-items: center;
justify-content: center;
align-content: space-between;
}
Фон, псевдоэлемент и т.п.