As a different font is likely to be already defined by the browser for form elements, here are 2 ways to use this font everywhere:
body, input, textarea {
font-family: Algerian;
}
body {
font-family: Algerian !important;
}
There'll still have a monospace font on elements like pre/code, kbd, etc but, in case you use these elements, you'd better use a monospace font there.
Important note: if very few people has this font installed on their OS, then the second font in the list will be used. Here you defined no second font so the default serif font will be used, and it'll be Times, Times New Roman except maybe on Linux.
Two options there: use @font-face if your font is free of use as a downloadable font or add fallback(s): a second, a third, etc and finally a default family (sans-serif, cursive (*), monospace or serif). The first of the list that exists on the OS of the user will be used.
(*) default cursive on Windows is Comic Sans. Except if you want to troll Windows users, don't do that :) This font is terrible except for your children birthdays where it's welcome.