You could use box-decoration-break
property with value of clone
.
box-decoration-break: clone;
Each box fragment is rendered independently with the specified border, padding and margin wrapping each fragment. The border-radius, border-image and box-shadow, are applied to each fragment independently. The background is drawn independently in each fragment which means that a background image with background-repeat: no-repeat may be repeated multiple times. – MDN
See the current browser support tables at caniuse.com
h1 {
font-weight: 800;
font-size: 5em;
line-height: 1.35em;
margin-bottom: 40px;
color: #fff;
}
h1 span {
background-color: rgba(0, 0, 0, 0.5);
padding: 0 20px;
-webkit-box-decoration-break: clone;
box-decoration-break: clone;
}
<h1><span>The quick brown fox jumps over the lazy dog.</span></h1>