How to resize form field for mobile on responsive site?

I'm using Cargo Collective to build a website and Tiny Letter's embed code for an email sign-up form. On mobile, the form field is the only thing on the page not resizing (see screenshot).

Mobile screenshot Desktop screenshot

I've compared the code of the field to the containers but not finding where it's breaking. Any help for this basic problem would be appreciated.

    <div>
<form>
<div>
93
input[type=button], input[type=submit], input[type=reset] {
  background-color:  #EE9862;
  border: none;
  color:  #414141;
  padding: 16px 32px;
  text-align: center;
  text-decoration: none;
  margin: 4px 2px;
  cursor: pointer;
  display: inline-block;
  font-size: 18px;
}
126Inherited from bodycopy.bodycopy.content.content_padding
[data-predefined-style="true"] bodycopy {
    font-size: 1.4rem;
    color:  #414141;
    font-family: A"Diatype Semi-Mono Variable", Icons;
    line-height: 1.3;
    letter-spacing: 0.05rem;
    font-style: normal;
    font-weight: 400;
    font-variation-settings: 'slnt' 0, 'MONO' 0.5;
    
}
222Inherited from div.page.container.container_width
[data-css-preset] .container {
    margin-left: auto /*!content_center*/;
    margin-right: auto /*!content_center*/;
    text-align: left /*!text_left*/;
}
5Inherited from body.homepage.editor-overlay-active.mobile.full_width
body {
    background-color:  #fff;
    color:  #000;
}