JSON Format to highlight text

Question

We have an SP List with a field that displays as a hyperlink. When clicked, a draft outlook email opens and shows a draft message that includes fields from the current item as well as some placeholders we'd like the user to update before sending. I'm seeking a way to highlight (in yellow?) those placeholders. In the code below the placeholders are in bold/italics. Any assistance is appreciated.

{

"$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",

"elmType": "a",

"attributes": {

"class": "sp-field-quickActions",

"href": {

"operator": "+",

"operands": [

"mailto:",

"[$RecruitingContact]",

"?subject=Referral for ",

"[$Company]",

" - ",

"[$Position]",

"&body=I would like to recommend [Enter Name of Candidate] for the ",

"[$Company]",

" - ",

"[$Position]",

" position.",

"\r\n",

"I am attaching their resume and providing a link to their LinkedIn profile. [Edit this sentence if no resume or link will be included.]",

"\r\n",

"[Please enter a brief statement of how you know and/or are related to the candidate.]"

]

}

},

"children": [

{

"elmType": "button",

"txtContent": "Refer a Friend",

"style": {

"background-color": "#E6E6FA",

"color": "#2F4F4F",

"width": "100%",

"font-weight": "bold"

}

}

]

}