After testing an example case with Firefox and Chrome, I would say the best option is to use declaration overflow: auto. Using overflow: hidden would make sense only if possible scrollbars are considered worse than losing user content.
The overflow: auto allows falling back to scrollbars automatically if content does not fit and it still forces clipping to selected element.
The declaration clip: rect(0,auto,auto,0); is no good because it only works with position: absolute; and without overflow: visible.
See an example without overflow: auto for an comparision.
Above examples inlined here as snippets:
An example without safeguards against Zalgo text:
body
{
background: #ccc;
color: #000;
font-family: sans-serif;
padding: 4em 1em;
}
section.userinput
{
margin-top: 0.5em;
padding: 0.1em 0.25em;
background: #fff;
border: solid #ccc 0.1em;
border-radius: 0.5em;
font-size: 120%;
}
.v1 section.userinput
{
overflow: auto;
}
.v2 section.userinput
{
position: absolute;
clip: rect(0em,auto,auto,0em);
}
<body class="">
<section class="userinput">
Some real content here.
</section>
<section class="userinput">
T̠̬̘̯̙̲̪̪͇̜̭̣̘̟̲͇̳̬͕̖̜̯̘͉͈͉͎̱͓̣̰̳̳͉̙̯̙̰͚͇͎͕̘̯̳̞̲̼̱̖̩͙͕̤͂̋͌ͤ̒ͬ̀͒͂͒ͩ̌͗̋̓ͭ́̀̿͒ͣͮ̓̋ͭ͊͒͐ͩ̆̓͂ͫ̐͂̇͛͑̓̚ͅẽ̗̙͚̮̭̮̬̠͈̻̦̭̭̳̹̯̹̦̔̌ͯ͂̎̈̊̍ͣ̿̈̈̿̄ͦͭ̍͑̽̎̅͛͗͐ͬ̂̊̽̌̎̋ͭ͆̈́̓ͦͦ̑͛ͯs̭̠͖̝͙̩̫̫̥̦͚̝̼̣̥̗ͣͦ͑́͐ͭ͊ͧ̽͐̈̔͛ͨ́̎̔ͤ͐͒̓̀̅̈́̊̋͋̀̿̎͒̉̽͂ͮͬt̾͒̂̽̐ͪ̆̾ͮ͌̽͛̌͒̔ͧ͗̿ͩ̄̿̿̌ͪͩ̊̏͑͌̀̋ͩ͆ͣ̑̏́̽̐͐̔ͪ̓̓ͭ͆ ̯̘͙̠̦̩̝͎̭̖̪̗̞̖̟̲͖̥͙͕̟̝̹͎̽o̼̮̭̞ͯͬ̀͐͗̿ͣ͛ͮͭ̎ͨ͒̌̾̐̉̍͗̎̈́̆ͪͦ̌ͧͦ̓ͨ̐ͯ͒͑͛ͯ̽ͅf̝̪̼̠͎͇̹̝̙̰̟̼͎̱͂ͩ̈́̌ͬ̒ͧ̽̅̉ͧ́͒̒͊ͦͭͭͭ͗́̽ͦ ͚̝̝̠̪͍̰̺̳̫̭͎͔̭̟͍͎͇͎͈͔̠̬͇̦͈̟̰̱̹̲̰̭̲̭̺̜͚̰̹̮̣̤̲̪̙̞͇̦͙͆ͪͨ̐ͨ̽̒͛ͩ̐ͤ͌̂́͒̌ͭͩͦ̎́̈ͬ̓̑̔͐̎͒̔̄ͥ̏ͥͯͧ͐ͪͧͥ̂ͬ̒̀̉̓ͭ̚ͅͅͅͅZ̘̥̲͍̠͎̱̺̘͈͍̟̤̠̮͖͉͕̙̩̲̣̠͎̥̣̜͚̜͕̻͔̰̞̫̭̹͕͙̝̠̮̣̰ͤͦ̍̓ͪͥ̒ͩ̋͆̍͋̽̅͗̈ͨ̂ͨ͋̔̔̓ͪͣ̅̇̏͒ͬ͐ͩ̇ͨ̋ͣ̌̔ͨ́ͪ̔̾̄ͤ̅͑̚ͅA̞̜̺̣͓̼̭̭͈̳̞͚̭̭͕̺͉̜̗̼̣̩̪͂ͯ̈́̍̍͛ͮ̂ͯ̽̎ͬͯ͆̋͌̍͐̌͗ͤ̒ͤ͊̐̈́ͧ̓̇ͬͦ̾ͭ̐̆̚ͅͅͅL̪͉̬̦̝̠̲͖̘̮̙̳͓͇͇̪̱͉̱͓̺͙͓̲̇́̍̽̇̎͊̍̐ͩ̔̋́ͬ̍ͮͫͮ͗̍͋ͭͯ̑̉̈́̄̾̂̀͆̅͑̽̃̚G̣̺̼͔̺̖̣̥̝̰͙̖͖̮̻̩͓̞͈̜̗̤̺̥̻̞͇̩͕̲̙̝̲̤̤̜̐͗͐ͦ̉͐͗ͩ̿ͩ̑ͫ̍͛̄ͦ̔̚O͇͎̬̰̦̜̻͔͇̖͇̞̪͉͉͔͕̥͇̬̮̰̠̟̤̰̹͖̗̺̙͍ͮͨ̿ͪͯ̈́ͫ̔̽̃̀ ̺͕̠̰̝͎̰̟̠̲̗͈̬̥͈͎̺̮̗͍̺͚̟̠̙̠̜̘̹͉̖̤͉̫̰̱̭̠̲̲̗͒ͥͯ̎͐ͨ̓̓ͮ͒ͧ̒̾́̍̍ͦͥ̈́͒͊̃̓̈̈́̀ͮ̂ͪ̓̄̏ͫ̄̓̓̿̓̔̋̎ͧͪͩͪ͋ͫt̘̥̳̺̳̟̯̜̱̯̬̣̣͔̬̟͈͖̗̹͉̫̯́̋͒͂̈́̎͐̇́ͫ̒͛ͥͦ̐̿͂͒͗̃ͮ͒ͪ̌͆̏ͯ̏ͯ̊ͣ̾̃͋ͩ̃̿͐e̹̠̻̟̪̪͎̭̭͎͎̮̹̬̮̪̓̑ͨ̐͐̈́̓ͤͦ͂̿̅͋ͭ̑̓ͬ͐͐ͤ͐ͪ̒ͥ̀̈́ͪ̇̆ͤ̏̏̄̾̌͒ͬ̊ͬ͛̄̄̌̍͋ͥͅͅx̪͇̞̫̰̠͓̣̻̯̞̭̙̝̣͉̱̘̤͇̦̘̙̥͚̫̩̲̘̻͈͉̱͙͇͙ͫ̐̌͛̓͛ͨ͒̂t̩̖̮̙̻ͬ͗͛̍̅̌ͧ͒ͫ̓ͮ̈͒̾ͮͣͮͨͪ͆ͥ̐̍ͮ̽̅̈́̿ͫ͐̍̉ͦͮ͆͗̔̎̿̇ͧ̋ͨͮ̐̓͑̽̑ͤ̊̚̚ͅ ̝͔̺̩͔͈̰͈̣̫̤͉͚͇̟̹̘͔͇̥̘̘̝͛͛̒ͭͣͮͥͦ̿̏ͥͦ̀͂̾͆ͯͧͮͤ͌̌́͗ͨ̎̒ͬ̈́ͧ̊ͨ̓͂̾̉͐ͦ̃̃̚ͅẖ̰̠̮͓̣̯̭̥̹̜̟͍͍͇̀ͧ̽͑̄͊̋̐͋ͨ̔ͭͬ́̀̐͌͗ͥ̓̇͗̂̊ͅe͇͙͕̺̖̰̟̠̩̘̪̳̻̳͉͔̺̳̲̦̘̞̬̬̝͓̬̣̟͕̘͓̬̍͗̋ͮ͑ͣ͗̓̓̎̈̃̾̊̃ͧ̊ͪ̃̀͋̋̄͑̈́̂́͒̔̎̎ͥ͛͌̃͒̈́ͤ͛ͬͫͪ̚r͉̮̼̙̩͖͍̗̣̘͚̭̩͙͙̻͓̦̱̣͉̮̲͇̥͉͚̲͕͖̩̦̫̪̬͔̟͔̦̻̼̼̫̫̯̣̮͈̺͓͖̬̂̾͛̉̆̍ͥ̈́̓̆ͫ͑̄̔̅̈̏̅̓ͨ͐̊ͮ̋̈́ͣͮ̋̓̾ͤ͊ͬ̀̑ͣ͊̇͌ͯ̚ͅḙ̲͍͙͕̯̘͓͔͔͈̹͈̗͎͕̬̖̟̖͚̳͎̖ͩ͊̃ͫ̔̓͒͗ͩ͋̂ͩͩͧ̍͛̿͒ͩͅ.̯̗͗̑̍̑͗ͫͦͦͪͪͧ́̾̓̌̉͑̊̌̿̓ͫ̆̑̽̽ͪͦͨ͌ͦͨ̓
</section>
<section class="userinput">
Some another real content here.
</section>
</body>
And example with safeguards against bleeding zalgo text:
With overflow: auto applied to each user input container (the only differences is the v1 class in body element; you could also try class v2 to understand why it doesn't work for this purpose):
body
{
background: #ccc;
color: #000;
font-family: sans-serif;
padding: 4em 1em;
}
section.userinput
{
margin-top: 0.5em;
padding: 0.1em 0.25em;
background: #fff;
border: solid #ccc 0.1em;
border-radius: 0.5em;
font-size: 120%;
}
.v1 section.userinput
{
overflow: auto;
}
.v2 section.userinput
{
position: absolute;
clip: rect(0em,auto,auto,0em);
}
<body class="v1">
<section class="userinput">
Some real content here.
</section>
<section class="userinput">
T̠̬̘̯̙̲̪̪͇̜̭̣̘̟̲͇̳̬͕̖̜̯̘͉͈͉͎̱͓̣̰̳̳͉̙̯̙̰͚͇͎͕̘̯̳̞̲̼̱̖̩͙͕̤͂̋͌ͤ̒ͬ̀͒͂͒ͩ̌͗̋̓ͭ́̀̿͒ͣͮ̓̋ͭ͊͒͐ͩ̆̓͂ͫ̐͂̇͛͑̓̚ͅẽ̗̙͚̮̭̮̬̠͈̻̦̭̭̳̹̯̹̦̔̌ͯ͂̎̈̊̍ͣ̿̈̈̿̄ͦͭ̍͑̽̎̅͛͗͐ͬ̂̊̽̌̎̋ͭ͆̈́̓ͦͦ̑͛ͯs̭̠͖̝͙̩̫̫̥̦͚̝̼̣̥̗ͣͦ͑́͐ͭ͊ͧ̽͐̈̔͛ͨ́̎̔ͤ͐͒̓̀̅̈́̊̋͋̀̿̎͒̉̽͂ͮͬt̾͒̂̽̐ͪ̆̾ͮ͌̽͛̌͒̔ͧ͗̿ͩ̄̿̿̌ͪͩ̊̏͑͌̀̋ͩ͆ͣ̑̏́̽̐͐̔ͪ̓̓ͭ͆ ̯̘͙̠̦̩̝͎̭̖̪̗̞̖̟̲͖̥͙͕̟̝̹͎̽o̼̮̭̞ͯͬ̀͐͗̿ͣ͛ͮͭ̎ͨ͒̌̾̐̉̍͗̎̈́̆ͪͦ̌ͧͦ̓ͨ̐ͯ͒͑͛ͯ̽ͅf̝̪̼̠͎͇̹̝̙̰̟̼͎̱͂ͩ̈́̌ͬ̒ͧ̽̅̉ͧ́͒̒͊ͦͭͭͭ͗́̽ͦ ͚̝̝̠̪͍̰̺̳̫̭͎͔̭̟͍͎͇͎͈͔̠̬͇̦͈̟̰̱̹̲̰̭̲̭̺̜͚̰̹̮̣̤̲̪̙̞͇̦͙͆ͪͨ̐ͨ̽̒͛ͩ̐ͤ͌̂́͒̌ͭͩͦ̎́̈ͬ̓̑̔͐̎͒̔̄ͥ̏ͥͯͧ͐ͪͧͥ̂ͬ̒̀̉̓ͭ̚ͅͅͅͅZ̘̥̲͍̠͎̱̺̘͈͍̟̤̠̮͖͉͕̙̩̲̣̠͎̥̣̜͚̜͕̻͔̰̞̫̭̹͕͙̝̠̮̣̰ͤͦ̍̓ͪͥ̒ͩ̋͆̍͋̽̅͗̈ͨ̂ͨ͋̔̔̓ͪͣ̅̇̏͒ͬ͐ͩ̇ͨ̋ͣ̌̔ͨ́ͪ̔̾̄ͤ̅͑̚ͅA̞̜̺̣͓̼̭̭͈̳̞͚̭̭͕̺͉̜̗̼̣̩̪͂ͯ̈́̍̍͛ͮ̂ͯ̽̎ͬͯ͆̋͌̍͐̌͗ͤ̒ͤ͊̐̈́ͧ̓̇ͬͦ̾ͭ̐̆̚ͅͅͅL̪͉̬̦̝̠̲͖̘̮̙̳͓͇͇̪̱͉̱͓̺͙͓̲̇́̍̽̇̎͊̍̐ͩ̔̋́ͬ̍ͮͫͮ͗̍͋ͭͯ̑̉̈́̄̾̂̀͆̅͑̽̃̚G̣̺̼͔̺̖̣̥̝̰͙̖͖̮̻̩͓̞͈̜̗̤̺̥̻̞͇̩͕̲̙̝̲̤̤̜̐͗͐ͦ̉͐͗ͩ̿ͩ̑ͫ̍͛̄ͦ̔̚O͇͎̬̰̦̜̻͔͇̖͇̞̪͉͉͔͕̥͇̬̮̰̠̟̤̰̹͖̗̺̙͍ͮͨ̿ͪͯ̈́ͫ̔̽̃̀ ̺͕̠̰̝͎̰̟̠̲̗͈̬̥͈͎̺̮̗͍̺͚̟̠̙̠̜̘̹͉̖̤͉̫̰̱̭̠̲̲̗͒ͥͯ̎͐ͨ̓̓ͮ͒ͧ̒̾́̍̍ͦͥ̈́͒͊̃̓̈̈́̀ͮ̂ͪ̓̄̏ͫ̄̓̓̿̓̔̋̎ͧͪͩͪ͋ͫt̘̥̳̺̳̟̯̜̱̯̬̣̣͔̬̟͈͖̗̹͉̫̯́̋͒͂̈́̎͐̇́ͫ̒͛ͥͦ̐̿͂͒͗̃ͮ͒ͪ̌͆̏ͯ̏ͯ̊ͣ̾̃͋ͩ̃̿͐e̹̠̻̟̪̪͎̭̭͎͎̮̹̬̮̪̓̑ͨ̐͐̈́̓ͤͦ͂̿̅͋ͭ̑̓ͬ͐͐ͤ͐ͪ̒ͥ̀̈́ͪ̇̆ͤ̏̏̄̾̌͒ͬ̊ͬ͛̄̄̌̍͋ͥͅͅx̪͇̞̫̰̠͓̣̻̯̞̭̙̝̣͉̱̘̤͇̦̘̙̥͚̫̩̲̘̻͈͉̱͙͇͙ͫ̐̌͛̓͛ͨ͒̂t̩̖̮̙̻ͬ͗͛̍̅̌ͧ͒ͫ̓ͮ̈͒̾ͮͣͮͨͪ͆ͥ̐̍ͮ̽̅̈́̿ͫ͐̍̉ͦͮ͆͗̔̎̿̇ͧ̋ͨͮ̐̓͑̽̑ͤ̊̚̚ͅ ̝͔̺̩͔͈̰͈̣̫̤͉͚͇̟̹̘͔͇̥̘̘̝͛͛̒ͭͣͮͥͦ̿̏ͥͦ̀͂̾͆ͯͧͮͤ͌̌́͗ͨ̎̒ͬ̈́ͧ̊ͨ̓͂̾̉͐ͦ̃̃̚ͅẖ̰̠̮͓̣̯̭̥̹̜̟͍͍͇̀ͧ̽͑̄͊̋̐͋ͨ̔ͭͬ́̀̐͌͗ͥ̓̇͗̂̊ͅe͇͙͕̺̖̰̟̠̩̘̪̳̻̳͉͔̺̳̲̦̘̞̬̬̝͓̬̣̟͕̘͓̬̍͗̋ͮ͑ͣ͗̓̓̎̈̃̾̊̃ͧ̊ͪ̃̀͋̋̄͑̈́̂́͒̔̎̎ͥ͛͌̃͒̈́ͤ͛ͬͫͪ̚r͉̮̼̙̩͖͍̗̣̘͚̭̩͙͙̻͓̦̱̣͉̮̲͇̥͉͚̲͕͖̩̦̫̪̬͔̟͔̦̻̼̼̫̫̯̣̮͈̺͓͖̬̂̾͛̉̆̍ͥ̈́̓̆ͫ͑̄̔̅̈̏̅̓ͨ͐̊ͮ̋̈́ͣͮ̋̓̾ͤ͊ͬ̀̑ͣ͊̇͌ͯ̚ͅḙ̲͍͙͕̯̘͓͔͔͈̹͈̗͎͕̬̖̟̖͚̳͎̖ͩ͊̃ͫ̔̓͒͗ͩ͋̂ͩͩͧ̍͛̿͒ͩͅ.̯̗͗̑̍̑͗ͫͦͦͪͪͧ́̾̓̌̉͑̊̌̿̓ͫ̆̑̽̽ͪͦͨ͌ͦͨ̓
</section>
<section class="userinput">
Some another real content here.
</section>
</body>
