1. admin.py에 Media class 추가

class ApiAreaRecvLogInline(admin.TabularInline):
    model = ApiAreaRecvLog
    extra = 0
    readonly_fields = ["aarl_dt", "getFromNowOn", "aarl_data"]

    class Media:
        css = {
            "all" : {"style/admin.css"}
        }

2. /static/style/ 에 admin/css파일 작성

@charset "utf-8";

.field-aarl_dt {
    width: 150px;
}

.field-getFromNowOn {
    width: 150px;
}