:root {
    color-scheme: dark;
    font-family: "Nunito", "Trebuchet MS", sans-serif;
    font-synthesis: none;
    text-rendering: optimizeLegibility;
    -webkit-font-smoothing: antialiased;
    --aqua: #00e9ed;
    --button: #04b4b3;
    --text: #f7fbfb;
}

* {
    box-sizing: border-box;
}

html {
    min-width: 320px;
    min-height: 100%;
    background: #000;
    scroll-behavior: smooth;
}

body {
    min-width: 320px;
    min-height: 100vh;
    margin: 0;
    color: var(--text);
    background:
        radial-gradient(ellipse at 42% 3%, rgba(0, 110, 105, .52), transparent 49%),
        linear-gradient(115deg, #005550 0%, #002b29 37%, #000 76%);
}

button,
a {
    font: inherit;
}

a {
    color: inherit;
    text-decoration: none;
}

.app-shell {
    display: flex;
    min-height: 100vh;
}

.sidebar {
    flex: 0 0 287px;
    width: 287px;
    min-height: 100vh;
    padding: 14px 5px 24px 0;
    border-right: 1px solid rgba(151, 199, 197, .13);
    background: linear-gradient(160deg, rgba(0, 51, 49, .85), rgba(0, 24, 23, .72));
}

.brand {
    display: block;
    width: max-content;
    margin: 0 auto;
    color: #fff;
    font-size: 24px;
    font-weight: 1000;
    letter-spacing: -.8px;
    line-height: 1.5;
}

.brand-accent,
.welcome h1 span,
.mobile-welcome p span {
    color: var(--aqua);
}

.sidebar-rule {
    height: 2px;
    margin: 20px 9px 38px 12px;
    background: var(--aqua);
}

.navigation {
    display: grid;
    gap: 11px;
}

.nav-link {
    display: flex;
    min-height: 53px;
    align-items: center;
    gap: 15px;
    padding: 0 29px;
    border: 1px solid #00cdd0;
    border-radius: 8px;
    color: #c6e1e1;
    background: rgba(0, 89, 85, .27);
    font-size: 17px;
    font-weight: 700;
    transition: background-color .18s ease, color .18s ease;
}

.nav-link:hover,
.nav-link.is-active {
    color: #e6ffff;
    background: rgba(0, 132, 127, .22);
}

.nav-link svg {
    width: 18px;
    height: 18px;
    flex: 0 0 auto;
    fill: none;
    stroke: currentColor;
    stroke-linecap: round;
    stroke-linejoin: round;
    stroke-width: 1.5;
}

.main-content {
    min-width: 0;
    flex: 1;
    padding: 34px 36px 60px;
}

.welcome > h1 {
    margin: 0 auto 65px;
    text-align: center;
    font-size: clamp(25px, 2.45vw, 34px);
    font-weight: 1000;
    letter-spacing: -.65px;
    line-height: 1.3;
}

.learning-card {
    padding: 12px 33px 17px;
    border: 1px solid rgba(199, 229, 228, .17);
    border-radius: 22px;
    background: linear-gradient(110deg, rgba(39, 67, 67, .78), rgba(45, 45, 45, .72));
    box-shadow: inset 0 1px 0 rgba(255, 255, 255, .04);
}

.card-copy h2 {
    margin: 0 0 1px;
    font-size: 24px;
    font-weight: 900;
    letter-spacing: .2px;
}

.progress-label {
    margin: 0;
    font-size: 17px;
    font-weight: 500;
}

.progress-track {
    height: 16px;
    margin-top: 6px;
    overflow: hidden;
    border-radius: 999px;
    background: #353542;
}

.progress-fill {
    display: block;
    width: 0;
    height: 100%;
    border-radius: inherit;
    background: var(--aqua);
    transition: width .3s ease;
}

.start-button {
    width: 100%;
    min-height: 54px;
    margin-top: 25px;
    border: 0;
    border-radius: 12px;
    color: #fff;
    background: var(--button);
    cursor: pointer;
    font-size: 26px;
    font-weight: 900;
    transition: background-color .18s ease, transform .18s ease;
}

.start-button:hover:not(:disabled) {
    background: #00c8c6;
    transform: translateY(-1px);
}

.start-button:focus-visible,
.menu-toggle:focus-visible,
.nav-link:focus-visible {
    outline: 3px solid #fff;
    outline-offset: 3px;
}

.start-button:disabled {
    cursor: default;
}

.mobile-header,
.mobile-welcome,
.menu-backdrop {
    display: none;
}

@media (min-width: 761px) {
    .sidebar {
        display: block;
    }
}

@media (max-width: 760px) {
    body {
        background:
            radial-gradient(ellipse at 20% 5%, rgba(0, 135, 129, .78), transparent 60%),
            linear-gradient(150deg, #00605b 0%, #002b29 48%, #000 88%);
    }

    .app-shell {
        display: block;
    }

    .sidebar {
        position: fixed;
        z-index: 5;
        top: 0;
        right: 0;
        display: block;
        width: min(56%, 410px);
        padding: 32px 0 24px 6px;
        border-right: 0;
        border-left: 1px solid rgba(180, 218, 216, .34);
        background: linear-gradient(160deg, rgba(0, 68, 65, .98), rgba(0, 25, 24, .98));
        transform: translateX(100%);
        transition: transform .25s ease;
        visibility: hidden;
    }

    .menu-open .sidebar {
        transform: translateX(0);
        visibility: visible;
    }

    .sidebar .brand {
        display: none;
    }

    .sidebar-rule {
        height: 4px;
        margin: 55px 46px 43px 41px;
    }

    .navigation {
        gap: 15px;
    }

    .nav-link {
        min-height: 75px;
        gap: 20px;
        padding: 0 44px;
        border-radius: 12px;
        font-size: 24px;
        white-space: nowrap;
    }

    .nav-link svg {
        width: 24px;
        height: 24px;
    }

    .main-content {
        padding: 34px 27px 48px;
    }

    .mobile-header {
        display: flex;
        align-items: center;
        justify-content: space-between;
    }

    .mobile-header .brand {
        margin: 0 0 0 20px;
        font-size: 34px;
        letter-spacing: -1px;
    }

    .menu-toggle {
        position: relative;
        z-index: 6;
        display: grid;
        width: 42px;
        height: 38px;
        align-content: center;
        justify-items: end;
        gap: 7px;
        padding: 0;
        border: 0;
        background: transparent;
        cursor: pointer;
    }

    .menu-toggle span {
        display: block;
        width: 36px;
        height: 3px;
        border-radius: 4px;
        background: #f4ffff;
        transition: transform .2s ease, opacity .2s ease;
    }

    .menu-toggle span:nth-child(2) {
        width: 30px;
    }

    .menu-open .menu-toggle span:first-child {
        transform: translateY(10px) rotate(45deg);
    }

    .menu-open .menu-toggle span:nth-child(2) {
        opacity: 0;
    }

    .menu-open .menu-toggle span:last-child {
        transform: translateY(-10px) rotate(-45deg);
    }

    .welcome > h1 {
        display: none;
    }

    .mobile-welcome {
        display: block;
        margin-top: 55px;
        text-align: center;
    }

    .mobile-welcome h1 {
        margin: 0;
        font-size: clamp(45px, 10vw, 66px);
        font-weight: 1000;
        letter-spacing: -2px;
        line-height: 1.05;
    }

    .mobile-welcome p {
        margin: 0;
        font-size: clamp(29px, 6.4vw, 45px);
        font-weight: 900;
        letter-spacing: .2px;
        line-height: 1.2;
        white-space: nowrap;
    }

    .learning-card {
        margin-top: 115px;
        padding: 14px 19px 25px;
        border-radius: 30px;
        text-align: center;
    }

    .card-copy h2 {
        margin-bottom: 5px;
        font-size: clamp(21px, 5vw, 34px);
        line-height: 1.25;
    }

    .progress-label {
        font-size: clamp(17px, 3.5vw, 24px);
    }

    .progress-track {
        height: 22px;
        margin-top: 10px;
    }

    .start-button {
        min-height: 75px;
        margin-top: 33px;
        border-radius: 18px;
        font-size: clamp(25px, 5.2vw, 34px);
    }

    .menu-backdrop {
        position: fixed;
        z-index: 4;
        inset: 0;
        display: block;
        background: transparent;
        opacity: 0;
        pointer-events: none;
        transition: opacity .2s ease;
    }

    .menu-open .menu-backdrop {
        opacity: 1;
        pointer-events: auto;
    }
}

@media (max-width: 430px) {
    .main-content {
        padding: 24px 18px 38px;
    }

    .mobile-header .brand {
        margin-left: 4px;
        font-size: 28px;
    }

    .mobile-welcome {
        margin-top: 58px;
    }

    .mobile-welcome h1 {
        font-size: clamp(39px, 11vw, 48px);
    }

    .mobile-welcome p {
        font-size: clamp(26px, 7vw, 31px);
    }

    .learning-card {
        margin-top: 105px;
        padding: 14px 15px 22px;
    }

    .sidebar {
        width: min(72%, 360px);
    }

    .nav-link {
        padding: 0 25px;
        font-size: 21px;
    }
}

@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        scroll-behavior: auto !important;
        transition-duration: .01ms !important;
    }
}