:root {
            color-scheme: dark;

            --background: #080e17;
            --surface: #101a28;
            --surface-light: #152337;
            --border: rgba(125, 170, 210, .13);

            --primary: #28b9ed;
            --primary-light: #65d9ff;
            --success: #35d69a;
            --warning: #f5b942;

            --text: #eaf3fc;
            --text-secondary: #91a5ba;
            --text-muted: #62788f;
        }

        * {
            margin: 0;
            padding: 0;
            box-sizing: border-box;
        }

        body {
            min-height: 100vh;
            background:
                radial-gradient(
                    circle at 50% -15%,
                    rgba(27, 139, 205, .19),
                    transparent 45%
                ),
                var(--background);

            color: var(--text);
            font-family: Arial, Helvetica, sans-serif;

            display: flex;
            justify-content: center;
        }

        button,
        a {
            font: inherit;
        }

        .tutorial-container {
            width: 100%;
            max-width: 760px;
            padding: 35px 22px 45px;
        }

        /* HEADER */

        .header {
            display: flex;
            align-items: center;
            justify-content: space-between;
            margin-bottom: 55px;
        }

        .brand {
            display: flex;
            align-items: center;
            gap: 12px;
        }

        .brand-icon {
            width: 43px;
            height: 43px;
            border-radius: 12px;

            display: grid;
            place-items: center;

            background: rgba(40, 185, 237, .12);
            border: 1px solid rgba(40, 185, 237, .3);

            color: var(--primary-light);
            font-size: 21px;
        }

        .brand-name {
            font-size: 14px;
            font-weight: 800;
            letter-spacing: 2px;
        }

        .brand-subtitle {
            margin-top: 4px;
            color: var(--text-muted);
            font-size: 10px;
            letter-spacing: 1.5px;
        }

        .version {
            color: var(--text-muted);
            font-size: 10px;
            letter-spacing: 1px;
        }

        /* HERO */

        .hero {
            text-align: center;
            margin-bottom: 45px;
        }

        .hero-label {
            display: inline-flex;
            align-items: center;
            gap: 8px;

            color: var(--primary-light);
            background: rgba(40, 185, 237, .09);

            border: 1px solid rgba(40, 185, 237, .2);
            border-radius: 30px;

            padding: 8px 13px;
            margin-bottom: 22px;

            font-size: 10px;
            font-weight: 700;
            letter-spacing: 1.5px;
        }

        .hero-label::before {
            content: "";
            width: 7px;
            height: 7px;
            border-radius: 50%;
            background: var(--success);
            box-shadow: 0 0 10px var(--success);
        }

        .hero h1 {
            font-size: clamp(30px, 7vw, 46px);
            line-height: 1.12;
            letter-spacing: -1.5px;
            margin-bottom: 17px;
        }

        .hero h1 span {
            color: var(--primary-light);
        }

        .hero p {
            max-width: 490px;
            margin: auto;

            color: var(--text-secondary);
            font-size: 14px;
            line-height: 1.8;
        }

        /* PTT DEMONSTRATION */

        .ptt-demo {
            position: relative;
            overflow: hidden;

            padding: 28px 20px;
            margin-bottom: 42px;

            text-align: center;

            background:
                linear-gradient(
                    145deg,
                    #14263b,
                    #0d1725
                );

            border: 1px solid rgba(40, 185, 237, .2);
            border-radius: 20px;
        }

        .ptt-demo::before {
            content: "";
            position: absolute;
            width: 180px;
            height: 180px;
            border-radius: 50%;

            background: rgba(40, 185, 237, .08);
            filter: blur(50px);

            top: -90px;
            left: calc(50% - 90px);
        }

        .ptt-label {
            position: relative;
            color: var(--text-secondary);
            font-size: 10px;
            font-weight: 700;
            letter-spacing: 2px;
        }

        .ptt-button {
            position: relative;

            width: 105px;
            height: 105px;
            margin: 24px auto 17px;

            display: grid;
            place-items: center;

            border-radius: 50%;

            background:
                linear-gradient(
                    145deg,
                    #168fc7,
                    #07547f
                );

            border: 5px solid rgba(112, 216, 255, .17);

            box-shadow:
                0 0 0 9px rgba(40, 185, 237, .06),
                0 0 35px rgba(40, 185, 237, .22);

            color: white;
            font-size: 32px;
        }

        .ptt-caption {
            position: relative;
            color: var(--primary-light);
            font-size: 12px;
            font-weight: 700;
            letter-spacing: 1px;
        }

        .ptt-description {
            position: relative;
            margin-top: 9px;
            color: var(--text-muted);
            font-size: 12px;
        }

        /* SECTION */

        .section-title {
            margin-bottom: 20px;
        }

        .section-title small {
            color: var(--primary);
            font-size: 10px;
            font-weight: 700;
            letter-spacing: 2px;
        }

        .section-title h2 {
            margin-top: 7px;
            font-size: 21px;
        }

        /* STEPS */

        .steps {
            display: grid;
            gap: 13px;
            margin-bottom: 42px;
        }

        .step {
            display: flex;
            gap: 17px;
            align-items: flex-start;

            padding: 19px;

            background: var(--surface);
            border: 1px solid var(--border);
            border-radius: 15px;
        }

        .step-number {
            flex-shrink: 0;

            width: 36px;
            height: 36px;

            display: grid;
            place-items: center;

            border-radius: 10px;

            background: rgba(40, 185, 237, .11);
            border: 1px solid rgba(40, 185, 237, .18);

            color: var(--primary-light);
            font-size: 13px;
            font-weight: 800;
        }

        .step-content h3 {
            font-size: 14px;
            margin: 2px 0 8px;
        }

        .step-content p {
            color: var(--text-secondary);
            font-size: 12px;
            line-height: 1.8;
        }

        /* STATUS */

        .status-section {
            margin-bottom: 42px;
        }

        .status-list {
            display: grid;
            grid-template-columns: repeat(2, 1fr);
            gap: 11px;
        }

        .status-card {
            padding: 16px;
            background: var(--surface);
            border: 1px solid var(--border);
            border-radius: 13px;
        }

        .status-indicator {
            display: inline-block;
            width: 8px;
            height: 8px;
            border-radius: 50%;
            margin-right: 7px;
        }

        .status-card strong {
            font-size: 12px;
        }

        .status-card p {
            margin-top: 9px;
            color: var(--text-secondary);
            font-size: 11px;
            line-height: 1.6;
        }

        .online { background: var(--success); }
        .transmitting { background: var(--primary); }
        .receiving { background: #a58bff; }
        .busy { background: var(--warning); }

        /* IMPORTANT NOTICE */

        .notice {
            display: flex;
            gap: 13px;
            align-items: flex-start;

            padding: 17px;

            background: rgba(245, 185, 66, .06);
            border: 1px solid rgba(245, 185, 66, .17);
            border-radius: 14px;

            margin-bottom: 35px;
        }

        .notice-icon {
            color: var(--warning);
            font-size: 18px;
        }

        .notice h3 {
            font-size: 12px;
            margin-bottom: 7px;
        }

        .notice p {
            color: var(--text-secondary);
            font-size: 11px;
            line-height: 1.8;
        }

        /* CTA */

        .cta {
            padding: 30px 20px;

            text-align: center;

            background:
                linear-gradient(
                    145deg,
                    rgba(21, 88, 125, .25),
                    rgba(13, 26, 41, .7)
                );

            border: 1px solid rgba(40, 185, 237, .2);
            border-radius: 19px;
        }

        .cta h2 {
            font-size: 22px;
            margin-bottom: 10px;
        }

        .cta p {
            color: var(--text-secondary);
            font-size: 12px;
            line-height: 1.7;
            margin-bottom: 23px;
        }

        .start-button {
            width: 100%;
            max-width: 310px;
            min-height: 52px;

            display: inline-flex;
            align-items: center;
            justify-content: center;
            gap: 12px;

            text-decoration: none;

            color: #06131c;
            background: var(--primary-light);

            border-radius: 12px;

            font-size: 12px;
            font-weight: 900;
            letter-spacing: 1.2px;

            box-shadow: 0 8px 25px rgba(40, 185, 237, .17);

            transition: .2s;
        }

        .start-button:hover {
            transform: translateY(-2px);
            background: white;
        }

        .start-button:active {
            transform: scale(.98);
        }

        /* FOOTER */

        .footer {
            text-align: center;
            padding-top: 32px;

            color: var(--text-muted);
            font-size: 10px;
            line-height: 1.8;
            letter-spacing: .6px;
        }

        @media(max-width: 420px) {

            .tutorial-container {
                padding: 25px 16px 35px;
            }

            .header {
                margin-bottom: 43px;
            }

            .version {
                font-size: 9px;
            }

            .step {
                padding: 16px;
            }

        }