for block elements:
<textarea style="width:100px; word-wrap:break-word;">
ACTGATCGAGCTGAAGCGCAGTGCGATGCTTCGATGATGCTGACGATGCTACGATGCGAGCATCTACGATCAGTC
</textarea>
for inline elements:
<span style="width:100px; word-wrap:break-word; display:inline-block;">
ACTGATCGAGCTGAAGCGCAGTGCGATGCTTCGATGATGCTGACGATGCTACGATGCGAGCATCTACGATCAGTC
</span>