Fankrai,
<!doctype html>
<html lang="ru">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style type="text/css">
.section-heading1--text .content{
display: none;
}
.section-heading1--text.more .content{
display: initial;
}
.section-heading1--text + .btn:after{
content: 'READ MORE'
}
.section-heading1--text.more + .btn:after{
content: 'HIDE'
}
</style>
<script>
document.addEventListener('click', ({target}) => {
if(target.closest('.btn')){
const prev = target.previousElementSibling;
prev.classList.toggle('more')
}
});
</script>
</head>
<body>
<p class="section-heading1--text">
Lorem ipsum dolor mero moleamet,
soluta euism od isea, hiea unereusams
ullu tpamco detore aer rper quo, utam
signiferuuue uo. Brute inani in prom in
<span class="content">Lorem ipsum dolor mero moleamet,
soluta euism od isea, hiea unereusams
ullu tpamco detore aer rper quo, utam
signiferuuue uo. Brute inani in prom in</span></p>
<button class="btn" type="button"></button>
<p class="section-heading1--text">
Lorem ipsum dolor mero moleamet,
soluta euism od isea, hiea unereusams
ullu tpamco detore aer rper quo, utam
signiferuuue uo. Brute inani in prom in
<span class="content">Lorem ipsum dolor mero moleamet,
soluta euism od isea, hiea unereusams
ullu tpamco detore aer rper quo, utam
signiferuuue uo. Brute inani in prom in</span></p>
<button class="btn" type="button"></button>
</body>
</html>