CSS: insert a line break

can you use css to add a line break

yes. use the pseudo-element ::before and ::after

then add content: "\A"; the backslash A is an escape meaning newline character.

then also add white-space: pre;

example

<div class="tFwMv">
some <span class="newlineHvDqy">thing</span>
</div>

.tFwMv {
 margin: 1rem;
 padding: 0.5rem;
 border: dotted 2px red;
}

.newlineHvDqy::before {
 content: "\A";
 white-space: pre;
}