JSON code: How to change Font Color to Black?

sangbui Use this JSON code: 

{
    "elmType": "div",
    "attributes": {
        "class": ""
    },
    "style": {
        "width": "99%",
        "border-top-width": "0px",
        "border-bottom-width": "1px",
        "border-left-width": "0px",
        "border-right-width": "0px",
        "border-style": "solid",
        "margin-bottom": "16px"
    },
    "children": [
        {
            "elmType": "div",
            "style": {
                "display": "flex",
                "box-sizing": "border-box",
                "align-items": "left"
            },
            "children": [
                {
                    "elmType": "div",
                    "attributes": {
                        "iconName": "link",
                        "class": "ms-fontSize-11 ms-fontWeight-regular",
                        "title": "Details"
                    },
                    "style": {
                        "flex": "none",
                        "padding": "0px",
                        "padding-left": "0px",
                        "height": "32px"
                    }
                }
            ]
        },
        {
            "elmType": "div",
            "attributes": {
                "class": "ms-fontWeight-bold ms-fontSize-11"
            },
            "style": {
                "box-sizing": "border-box",
                "width": "100%",
                "text-align": "left",
                "padding": "21px 12px",
                "overflow": "hidden"
            },
            "children": [
                {
                    "elmType": "a",
                    "style": {
                        "color": "black"
                    },
                    "txtContent": "In case you register for more than one person, please click and fill in this form then attach it to Attachments field ",
                    "attributes": {
                        "href": "https://jabil-my.sharepoint.com/:x:/p/sang_bui1127/EZAox0Ik7wZMvmPk2aFSzzUBGMUr0ChjRAqa8G2zH_cXZw?e=...",
                        "target": "_blank"
                    }
                }
            ]
        }
    ]
}

Output: 

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