Basic form styles are give below - field comes with three sizes. By default all form fields are 100% width - so it's depends on container size. Form input's have default style, hover and focus style.
<div class="form-field form-field-search small">
<i class="form-field-search-icon ion-search"></i>
<input type="text" name="" class="form-input" placeholder="Search ...">
</div>
<div class="form-field form-field-search">
<i class="form-field-search-icon ion-search"></i>
<input type="text" name="" class="form-input" placeholder="Search ...">
</div>
<div class="form-field form-field-search large">
<i class="form-field-search-icon ion-search"></i>
<input type="text" name="" class="form-input" placeholder="Search ...">
</div>
<div class="form-field form-field-search loading">
<i class="form-field-search-icon ion-search"></i>
<input type="text" name="" class="form-input" placeholder="Search ...">
<i class="form-field-search-loading-icon"></i>
</div>
<div class="form-field form-field-search loading hint">
<i class="form-field-search-icon ion-search"></i>
<input type="text" name="" class="form-input" placeholder="Search ...">
<i class="form-field-search-loading-icon"></i>
<div class="form-field-search-hint">
<ul>
<li><a href="#">Afganistan</a></li>
<li><a href="#">Srilanka <span class="badge badge-info">new</span></a></li>
<li><a href="#">Bangladesh</a></li>
<li><a href="#">United state</a></li>
</ul>
</div>
</div>
If you're looking for tag implementation, then see this.
Reference from _form.scss
$form-input-placeholder-color: lighten(map-get($colors, dark), 60%) !default;
$form-input-border-color: lighten(map-get($colors, dark), 70%) !default;
$form-input-hover-border-color: map-get($colors, link) !default;
$form-input-focus-border-color: map-get($colors, primary) !default;
$form-text-color: lighten(map-get($colors, dark), 50%) !default;
$form-input-radius: rem(2) !default;
$form-checkbox-label-color: lighten(map-get($colors, dark), 20%) !default;
$form-disable-input-color: darken(map-get($colors, white), 5%) !default;
$form-primary-color: darken(map-get($colors, white), 6%) !default;
$form-primary-hover-color: map-get($colors, info) !default;
$form-primary-focus-color: map-get($colors, white) !default;
$form-error-color: map-get($colors, danger) !default;
$form-success-color: map-get($colors, success) !default;
$form-warning-color: map-get($colors, info) !default;