SOLVED
Hey Megan, you can move text inside the fields using the HINT TEXT input in the form editor
Hey Michelle-
I've setup a basic template to house an example of the form here: FLEX Form CSS - Digital Pi
The CSS for this form is included below, you should be able to copy/paste this into the Custom CSS on your form to put it into play on your end.
It'd probably be best to clone your live form and apply these changes to the clone to test before you implement it. You can also copy/paste the existing Custom CSS into a word doc or simple text editor to save as a backup.
Here's a quick look at where to find the Custom CSS on your form:
You'll also need to do a little work in the Field Details tab to create the fieldsets and place your fields into them. I've included a shot below of what the setup looks like on my end (and there's also an annotated copy of this on the live example linked above). You can create a new fieldset the same way you'd add a new field/rich text to the form and then drag-and-drop the fields into the middle of the fieldset. I've labeled each fieldset in the editor so it makes a little more sense to anyone coming along in the future who isn't as familiar with the setup. These labels (legends) are hidden in the live view, so they can be used to hold comments/info as you see fit.
*NOTE: For the sake of keeping this inline with this example, this form IS NOT styled to accommodate other inputs like a checkbox or radio (anything that doesn't currently exist on the form). Those will need a more specific set of styles, maybe something to tackle or add-on down the road. I've tested on Chrome, Firefox, IE 11 and Safari (mobile and desktop) to be sure this'll work out without a hitch, please let me know if you come across anything that's acting weird.
/* all form elements */
form.mktoForm * {
font-size: 1em !important;
font-family: 'Open Sans', "Helvetica Neue", Helvetica, Arial, sans-serif!important;
-webkit-box-sizing: border-box;
box-sizing: border-box;
}
/* color outline and border for active elements */
form.mktoForm * {outline-color: #e7781e !important;}
form.mktoForm *:focus {border-color: #e7781e !important;}
/* full-width (fluid) elements */
form.mktoForm,
form.mktoForm .mktoButtonRow,
form.mktoForm fieldset .mktoFormRow,
form.mktoForm fieldset .mktoFormCol,
form.mktoForm fieldset .mktoFieldWrap,
form.mktoForm fieldset .mktoFormRow input,
form.mktoForm fieldset .mktoFormRow select,
form.mktoForm fieldset .mktoFormRow textarea {
width: 100% !important;
}
}
/* fixed width element reset */
form.mktoForm .mktoHasWidth {
width: auto !important;
}
/* hide these elements (spacers, legend, labels) */
.mktoOffset,
.mktoGutter,
form.mktoForm fieldset legend,
form.mktoForm label.mktoLabel {
display: none !important;
}
/* ----------------------------------- */
/* ==========[Form Elements]========== */
/* ----------------------------------- */
/* fieldset (all) */
form.mktoForm fieldset {
width: 100% !important;
padding: 0px !important;
margin: 0px !important;
border: none !important;
}
/* inputs, textarea, select */
.mktoForm input[type=url],
.mktoForm input[type=text],
.mktoForm input[type=date],
.mktoForm input[type=tel],
.mktoForm input[type=email],
.mktoForm input[type=number],
.mktoForm textarea.mktoField,
.mktoForm select.mktoField {
height: auto !important;
line-height: inherit !important;
font-size: inherit !important;
-webkit-appearance: none!important;
background-color: #fff;
background: #fff;
color: #333!important;
border: 1px solid #ccc;
-webkit-box-shadow: 0 1px 2px rgba(0, 0, 0, 0.1) inset;
box-shadow: 0 1px 2px rgba(0, 0, 0, 0.1) inset;
border-radius: 0px!important;
padding: 10px!important;
-webkit-box-shadow: none!important;
box-shadow: none!important;
-webkit-transition: all 250ms ease-out!important;
-o-transition: all 250ms ease-out!important;
transition: all 250ms ease-out!important;
width: 100%!important;
}
/* invalid fields */
.mktoForm input.mktoField.mktoInvalid, .mktoForm select.mktoField.mktoInvalid, .mktoForm textarea.mktoField.mktoInvalid, .mktoForm div.mktoLogicalField.mktoInvalid {
border: 1px solid #c00;
}
/* rich text */
form.mktoForm .mktoHtmlText {
padding: 0.5rem 0px 1.25rem 0px !important;
width: 100% !important;
text-align: left !important;
font-family: "Open Sans", "Helvetica", Helvetica, Arial, sans-serif;
font-size: 16px;
}
/* button */
form.mktoForm .mktoButtonWrap {
margin-left: 0px !important;
}
form.mktoForm .mktoButtonWrap .mktoButton {
background-image: -webkit-gradient(linear, left top, left bottom, from(#e7781e), to(#e7781e))!important;
background-image: -webkit-linear-gradient(top, #e7781e, #e7781e)!important;
background-image: -o-linear-gradient(top, #e7781e, #e7781e)!important;
background-image: linear-gradient(to bottom, #e7781e, #e7781e)!important;
border: 1px solid #e7781e!important;
border-radius: 4px!important;
background-color: #e7781e!important;
padding: 10px!important;
width: 100% !important;
text-transform: uppercase!important;
font-family: 'Open Sans', "Helvetica Neue", Helvetica, Arial, sans-serif !important;
font-size: 16px !important;
font-weight: 300 !important;
letter-spacing: 2px !important;
color: #ffffff !important;
min-height: 35px !important;
margin: 0 auto !important;
}
/* ------------------------------------ */
/* ==========[Responsive CSS]========== */
/* ------------------------------------ */
/* for landscape mobile and up */
@media screen and (min-width:576px) {
/* unstack form */
form.mktoForm {
display: -webkit-box !important;
display: -ms-flexbox !important;
display: flex !important;
-ms-flex-wrap: wrap;
flex-wrap: wrap;
}
/* Row 1 & 2 (filedset rows) to columns */
form.mktoForm>.mktoFormRow:nth-of-type(1),
form.mktoForm>.mktoFormRow:nth-of-type(2) {
width: 50% !important;
float: left !important;
clear: none !important;
}
/* column padding */
form.mktoForm fieldset .mktoFormCol .mktoFieldWrap {
padding: 0 10px !important;
}
/* fieldset (all) */
form.mktoForm .mktoFormRow fieldset {
-webkit-box-flex: 1;
-ms-flex-positive: 1;
flex-grow: 1;
height: 100%;
}
/* 2nd Column - fieldset 2 */
form.mktoForm .mktoFormRow:nth-of-type(2) fieldset .mktoFormRow,
form.mktoForm .mktoFormRow:nth-of-type(2) fieldset .mktoFormRow .mktoFormCol,
form.mktoForm .mktoFormRow:nth-of-type(2) fieldset .mktoFormRow .mktoFormCol .mktoFieldWrap {
display: -webkit-box !important;
display: -ms-flexbox !important;
display: flex !important;
height: 100% !important;
}
/* textarea | SPECIFIC ELEMENT CSS: grow textarea in 2nd column */
form.mktoForm textarea.mktoField {
margin-bottom: 10px;
height: calc(100% - 10px);
}
/* rich text */
form.mktoForm .mktoHtmlText {
font-weight: 400 !important;
padding: 1.25rem 10px !important;
}
/* button */
form.mktoForm .mktoButtonRow {
clear: both;
}
form.mktoForm .mktoButtonWrap {
margin-left: 10px !important;
}
form.mktoForm .mktoButtonWrap .mktoButton {
min-width: 210px !important;
width: auto !important;
}
}
Quick Walkthru:
1. Clone Form, backup current CSS, apply new CSS - You can copy/paste the CSS above into the Custom CSS on your new form once that's setup.
2. Create a test LP to host the embedded form in your CMS - Maybe you can just clone this landing page and add the embded code for your new form into the page for testing/review. *Note: If you're already using a test page for this, you can just use the new embed code in place of the old code - the idea is that you'll want to test this in a staging environment instead of on the live page.
3. Apply styles to live form - Once everything looks good / is tested, you can simply copy/paste the CSS above in place of the existing CSS on your form and approve the form to see the updates on your live page.
Let me know if you run into anything you've got questions on, and I hope this ends up helping you accomplish what you were after.
High Five! and Happy Friday 
p.s. this should still work if you were to add more fields to the left column, just in case
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