styles.css

@import url('https://fonts.googleapis.com/css2?family=Nunito:wght@500;700;800&display=swap');

:root {
    --bg: #f4fbff;
    --bg-accent: #e7f5ff;
    --surface: #ffffff;
    --surface-soft: #f8fbff;
    --text: #103248;
    --text-muted: #4b6476;
    --primary: #0ea5a3;
    --primary-strong: #0b7f7d;
    --secondary: #1184dc;
    --secondary-strong: #0d63a5;
    --danger: #e24d4d;
    --success: #16a34a;
    --shadow: 0 14px 32px rgba(16, 50, 72, 0.14);
    --radius: 18px;
    --radius-sm: 10px;
    --touch-target: 44px;
}

* {
    box-sizing: border-box;
}

body {
    font-family: 'Nunito', 'Segoe UI', Tahoma, sans-serif;
    background: radial-gradient(circle at 15% 15%, #ffffff, var(--bg-accent) 38%, var(--bg) 100%);
    color: var(--text);
    margin: 0;
    padding: 20px;
    padding-bottom: calc(92px + env(safe-area-inset-bottom));
    display: flex;
    flex-direction: column;
    align-items: center;
    min-height: 100vh;
    -webkit-text-size-adjust: 100%;
}

.main-content {
    display: flex;
    gap: 20px;
    align-items: flex-start;
    max-width: 1200px;
    width: 100%;
    margin-bottom: 50px;
    position: relative;
}

.problem-area {
    flex: 1;
    min-width: 0;
}

.container {
    width: 100%;
    text-align: center;
    max-width: 1000px;
    margin: 0 auto;
    padding: 20px;
}

.header-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    width: 100%;
    padding: 0 20px;
    max-width: 1000px;
    margin: 0 auto 20px auto;
    gap: 14px;
}

h1 {
    text-align: center;
    margin: 0 auto;
    font-size: clamp(1.7rem, 2.3vw, 2.2rem);
    flex-grow: 1;
    padding: 0 20px;
    color: var(--text);
}

.home-button,
.toggle-scratchpad,
.nav-button,
.scratchpad-button {
    border: 0;
    color: #ffffff;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font: inherit;
    font-weight: 700;
    transition: transform 0.2s ease, filter 0.2s ease;
    min-height: var(--touch-target);
}

.home-button,
.toggle-scratchpad {
    padding: 12px 20px;
    font-size: 16px;
    background-color: var(--secondary);
    text-decoration: none;
    display: inline-flex;
    align-items: center;
    min-width: 136px;
    justify-content: center;
}

.home-button:hover,
.toggle-scratchpad:hover {
    background-color: var(--secondary-strong);
    transform: translateY(-1px);
}

.problem {
    font-size: clamp(1.25rem, 2.2vw, 1.8rem);
    margin: 30px auto;
    padding: 30px;
    background-color: var(--surface);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    max-width: 900px;
    overflow-wrap: anywhere;
}

.options {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    gap: 20px;
    margin: 30px auto;
    max-width: 900px;
    padding: 0 20px;
}

.option {
    padding: 22px;
    font-size: clamp(1.05rem, 2vw, 1.5rem);
    background-color: var(--primary);
    color: #ffffff;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    transition: transform 0.2s ease, filter 0.2s ease;
    width: 100%;
    text-align: center;
    font-family: inherit;
    font-weight: 700;
    min-height: 56px;
    display: inline-flex;
    align-items: center;
    justify-content: center;
}

.option:hover {
    transform: translateY(-2px);
    filter: brightness(0.95);
}

.option.wrong {
    background-color: var(--danger);
    animation: shake 0.5s;
}

.option.correct {
    background-color: var(--success);
    animation: correct 0.5s;
}

.clock-container {
    display: flex;
    justify-content: center;
    align-items: center;
    margin-top: 20px;
}

.analog-clock {
    width: 250px;
    height: 250px;
    border: 5px solid #1f3342;
    border-radius: 50%;
    position: relative;
    background-color: var(--surface);
    box-shadow: 0 8px 16px rgba(0, 0, 0, 0.15);
}

.clock-face {
    width: 100%;
    height: 100%;
    position: relative;
}

.clock-center {
    position: absolute;
    top: 50%;
    left: 50%;
    width: 10px;
    height: 10px;
    background-color: #1f3342;
    border-radius: 50%;
    transform: translate(-50%, -50%);
    z-index: 10;
}

.clock-hand {
    position: absolute;
    bottom: 50%;
    left: 50%;
    background-color: #1f3342;
    transform-origin: bottom center;
    border-radius: 5px;
}

.hour-hand {
    width: 6px;
    height: 30%;
    transform: translateX(-50%) rotate(0deg);
    z-index: 8;
}

.minute-hand {
    width: 4px;
    height: 40%;
    transform: translateX(-50%) rotate(0deg);
    z-index: 9;
    background-color: #3a5669;
}

.clock-number {
    position: absolute;
    width: 30px;
    height: 30px;
    text-align: center;
    line-height: 30px;
    font-size: 18px;
    font-weight: 700;
    color: #1f3342;
    cursor: pointer;
    user-select: none;
    border-radius: 50%;
    transition: background-color 0.2s, color 0.2s;
}

.clock-number:hover {
    background-color: #edf6ff;
}

.clock-number.selected,
.clock-number.correct {
    background-color: var(--success);
    color: #ffffff;
}

.clock-number.wrong {
    background-color: var(--danger);
    color: #ffffff;
    animation: shake 0.5s;
}

.clock-read-layout {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 20px;
    margin: 30px auto;
    max-width: 900px;
}

.clock-read-options {
    width: 100%;
    margin: 0;
    padding: 0 20px;
}

.clock-number-static {
    cursor: default;
}

.clock-number-static:hover {
    background-color: transparent;
}

.clock-tick {
    position: absolute;
    left: 50%;
    top: 6px;
    transform-origin: 50% 119px;
    background-color: #1f3342;
    z-index: 2;
}

.minute-tick {
    width: 2px;
    height: 8px;
}

.hour-tick {
    width: 3px;
    height: 14px;
}

.navigation {
    margin: 30px auto;
    text-align: center;
    display: flex;
    justify-content: center;
    gap: 20px;
}

.nav-button {
    padding: 14px 26px;
    font-size: 17px;
    background-color: var(--secondary);
    min-width: 150px;
}

.nav-button:hover {
    background-color: var(--secondary-strong);
    transform: translateY(-1px);
}

.nav-button:disabled {
    background-color: #c2ced6;
    cursor: not-allowed;
    transform: none;
}

.scratchpad-area {
    display: none;
    width: min(350px, 100%);
    min-height: 550px;
    background: var(--surface);
    border-radius: var(--radius);
    box-shadow: var(--shadow);
    padding: 10px;
}

.scratchpad-area.open {
    display: block;
}

.scratchpad-controls {
    display: flex;
    gap: 10px;
    margin-bottom: 10px;
    justify-content: center;
    flex-wrap: wrap;
}

.scratchpad-button {
    padding: 8px 15px;
    font-size: 15px;
    background-color: var(--primary);
    display: flex;
    align-items: center;
    gap: 5px;
    min-height: var(--touch-target);
}

.scratchpad-button:hover {
    background-color: var(--primary-strong);
    transform: translateY(-1px);
}

.scratchpad-button.clear {
    background-color: var(--danger);
}

.scratchpad-button.clear:hover {
    background-color: #be2f2f;
}

.scratchpad-canvas {
    width: 100%;
    height: 500px !important;
    min-height: 500px;
    border: 2px solid #d7e4ee;
    border-radius: 8px;
    touch-action: none;
    cursor: crosshair;
    background-color: #ffffff;
    display: block;
}

.problem-type {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background-color: rgba(255, 255, 255, 0.95);
    backdrop-filter: blur(4px);
    padding: 10px;
    padding-bottom: calc(10px + env(safe-area-inset-bottom));
    font-size: 14px;
    color: var(--text-muted);
    text-align: center;
    border-top: 2px solid var(--primary);
    box-shadow: 0 -2px 8px rgba(0, 0, 0, 0.08);
}

.stars {
    position: fixed;
    width: 100%;
    height: 100%;
    pointer-events: none;
    z-index: 9999;
}

.star {
    position: absolute;
    color: #f59e0b;
    font-size: 30px;
    animation: star-fall 1s ease-out forwards;
}

.confetti {
    position: absolute;
    width: 10px;
    height: 20px;
    animation: confetti-fall 3s ease-out forwards;
}

.heart {
    position: absolute;
    color: var(--danger);
    font-size: 24px;
    animation: heart-float 2s ease-out forwards;
}

.sparkle {
    position: absolute;
    color: #facc15;
    font-size: 20px;
    animation: sparkle-spin 1.5s ease-out forwards;
}

.balloon {
    position: absolute;
    font-size: 40px;
    animation: balloon-float 4s ease-out forwards;
}

.firework-spark {
    position: absolute;
    width: 8px;
    height: 8px;
    border-radius: 999px;
    box-shadow: 0 0 10px rgba(255, 255, 255, 0.85);
    animation: firework-burst 0.9s ease-out forwards;
}

@keyframes star-fall {
    0% {
        transform: translateY(-50px) rotate(0deg);
        opacity: 1;
    }
    100% {
        transform: translateY(100vh) rotate(360deg);
        opacity: 0;
    }
}

@keyframes confetti-fall {
    0% {
        transform: translateY(-10px) rotate(0deg);
        opacity: 1;
    }
    25% {
        transform: translateY(25vh) rotate(90deg) translateX(20px);
    }
    50% {
        transform: translateY(50vh) rotate(180deg) translateX(-20px);
    }
    75% {
        transform: translateY(75vh) rotate(270deg) translateX(20px);
    }
    100% {
        transform: translateY(100vh) rotate(360deg);
        opacity: 0;
    }
}

@keyframes heart-float {
    0% {
        transform: translateY(0) scale(1);
        opacity: 1;
    }
    50% {
        transform: translateY(-50vh) scale(1.5);
        opacity: 0.5;
    }
    100% {
        transform: translateY(-100vh) scale(0.5);
        opacity: 0;
    }
}

@keyframes sparkle-spin {
    0% {
        transform: rotate(0deg) scale(1);
        opacity: 1;
    }
    50% {
        transform: rotate(180deg) scale(1.5);
        opacity: 0.5;
    }
    100% {
        transform: rotate(360deg) scale(0.5);
        opacity: 0;
    }
}

@keyframes balloon-float {
    0% {
        transform: translateY(0) translateX(0);
        opacity: 1;
    }
    25% {
        transform: translateY(-25vh) translateX(20px);
    }
    50% {
        transform: translateY(-50vh) translateX(-20px);
    }
    75% {
        transform: translateY(-75vh) translateX(20px);
    }
    100% {
        transform: translateY(-100vh) translateX(0);
        opacity: 0;
    }
}

@keyframes firework-burst {
    0% {
        transform: translate(0, 0) scale(1);
        opacity: 1;
    }
    100% {
        transform: translate(var(--dx, 0), var(--dy, 0)) scale(0.2);
        opacity: 0;
    }
}

@keyframes shake {
    0%,
    100% {
        transform: translateX(0);
    }
    25% {
        transform: translateX(-10px);
    }
    75% {
        transform: translateX(10px);
    }
}

@keyframes correct {
    0% {
        transform: scale(1);
    }
    50% {
        transform: scale(1.1);
    }
    100% {
        transform: scale(1);
    }
}

.home-page {
    justify-content: center;
    position: relative;
    overflow-x: hidden;
    padding-bottom: 20px;
    background:
        radial-gradient(circle at 10% 15%, rgba(14, 165, 163, 0.22), transparent 26%),
        radial-gradient(circle at 85% 12%, rgba(17, 132, 220, 0.18), transparent 24%),
        radial-gradient(circle at 80% 85%, rgba(250, 204, 21, 0.18), transparent 28%),
        linear-gradient(180deg, #f9fdff 0%, #eef8ff 50%, #f4fbff 100%);
}

.home-page::before {
    content: "";
    position: fixed;
    inset: 0;
    z-index: 0;
    pointer-events: none;
    opacity: 0.38;
    background-image:
        linear-gradient(rgba(17, 132, 220, 0.1) 1px, transparent 1px),
        linear-gradient(90deg, rgba(17, 132, 220, 0.1) 1px, transparent 1px);
    background-size: 36px 36px;
}

.home-container {
    max-width: 1100px;
    padding-bottom: 40px;
    position: relative;
    z-index: 1;
}

.home-header {
    margin: 0 auto 30px auto;
    max-width: 760px;
    text-align: center;
}

.home-kicker {
    margin: 0 0 6px 0;
    font-size: 0.9rem;
    letter-spacing: 0.14em;
    text-transform: uppercase;
    color: var(--secondary);
    font-weight: 800;
}

.home-subtitle {
    color: var(--text-muted);
    margin: 10px auto 0 auto;
    font-size: 1.05rem;
}

.catalog-grid {
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 20px;
}

.topic-section {
    background-color: var(--surface);
    border-radius: var(--radius);
    padding: 20px;
    margin-bottom: 0;
    box-shadow: var(--shadow);
}

.topic-title {
    color: var(--primary-strong);
    font-size: 1.3rem;
    margin: 0 0 16px 0;
}

.problem-links {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.problem-link {
    display: flex;
    align-items: center;
    gap: 10px;
    padding: 14px 16px;
    background-color: var(--primary);
    color: #ffffff;
    text-decoration: none;
    border-radius: 12px;
    transition: transform 0.2s ease, filter 0.2s ease;
    font-size: 1.05rem;
    font-weight: 700;
    min-height: var(--touch-target);
}

.problem-link:hover {
    transform: translateY(-2px);
    filter: brightness(0.96);
}

.problem-icon {
    display: inline-flex;
    min-width: 1.4rem;
}

.coming-soon {
    background-color: #dce7ee;
    color: #688093;
    cursor: default;
}

.coming-soon:hover {
    transform: none;
    filter: none;
}

.new-badge {
    margin-left: auto;
    color: #8a2000;
    font-weight: 800;
    font-size: 0.72rem;
    letter-spacing: 0.03em;
    text-transform: uppercase;
    background-color: #ffe07a;
    padding: 2px 8px;
    border-radius: 999px;
}

.noscript-note {
    text-align: center;
    color: var(--text-muted);
}

.flashcard-page-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    min-height: 300px;
}

.flashcard-container {
    perspective: 1000px;
    width: min(350px, 92vw);
    height: 200px;
    margin-bottom: 20px;
}

.flashcard {
    width: 100%;
    height: 100%;
    position: relative;
    transform-style: preserve-3d;
    transition: transform 0.6s;
    box-shadow: var(--shadow);
    border-radius: 10px;
}

.flashcard.is-flipped {
    transform: rotateY(-180deg);
}

.flashcard-front,
.flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: clamp(1.9rem, 7vw, 2.5rem);
    font-weight: 700;
    border-radius: 10px;
    padding: 15px;
    text-align: center;
}

.flashcard-front {
    background-color: #f0faff;
    color: #1f3342;
}

.flashcard-back {
    background-color: #ddf0ff;
    color: #0d63a5;
    transform: rotateY(-180deg);
}

.flashcard-navigation {
    margin-top: 15px;
}

.flashcard-navigation .nav-button {
    padding: 10px 20px;
    font-size: 1em;
    width: 100px;
    text-align: center;
}

.problem-area > .container.flashcard-page-container {
    display: flex;
}

.orientation-toggle {
    display: flex;
    align-items: center;
    gap: 0;
    background-color: #deecf7;
    border-radius: 30px;
    padding: 3px;
    position: relative;
    box-shadow: inset 0 1px 3px rgba(0, 0, 0, 0.1);
}

.toggle-label {
    font-size: 14px;
    font-weight: 700;
    color: #34607d;
    padding: 6px 12px;
    border-radius: 25px;
    cursor: pointer;
    position: relative;
    z-index: 1;
    transition: color 0.3s ease;
}

.switch {
    position: absolute;
    opacity: 0;
    height: 0;
    width: 0;
}

.toggle-label.active {
    color: #ffffff;
}

.slider-bg {
    position: absolute;
    height: calc(100% - 6px);
    width: 50%;
    background-color: var(--secondary);
    border-radius: 25px;
    transition: transform 0.3s ease;
    z-index: 0;
    top: 3px;
    left: 3px;
}

.slider-bg.vertical {
    transform: translateX(100%);
}

.slider,
.slider:before,
input:checked + .slider,
input:focus + .slider,
input:checked + .slider:before,
.slider.round,
.slider.round:before {
    display: none;
}

.flashcard-container.vertical {
    width: min(200px, 64vw);
    height: 350px;
}

.flashcard.vertical .flashcard-front,
.flashcard.vertical .flashcard-back {
    flex-direction: column;
    align-items: center;
    justify-content: center;
    line-height: 1.2;
}

.flashcard.vertical .flashcard-front span {
    width: auto;
    padding-right: 0;
}

.flashcard.vertical .flashcard-front .num-line {
    display: block;
    text-align: right;
    width: 5ch;
    margin: 0 auto;
    padding: 0;
    line-height: 1.3;
}

.flashcard.vertical .flashcard-front .op-line {
    display: block;
    border-bottom: 2px solid #1f3342;
    margin: 2px auto 5px auto;
    width: 5ch;
}

.flashcard.vertical .flashcard-back span {
    text-align: center;
}

@media (max-width: 900px) {
    .catalog-grid {
        grid-template-columns: 1fr;
    }
}

@media (max-width: 1024px) {
    body {
        padding: 16px;
        padding-bottom: calc(92px + env(safe-area-inset-bottom));
    }

    .main-content {
        flex-direction: column;
        gap: 16px;
        margin-bottom: 72px;
    }

    .header-container {
        flex-direction: column;
        align-items: stretch;
        gap: 10px;
        padding: 0 10px;
    }

    h1 {
        padding: 0;
    }

    .home-button,
    .toggle-scratchpad {
        width: 100%;
        max-width: 420px;
        margin: 0 auto;
    }

    .orientation-toggle {
        width: 100%;
        max-width: 420px;
        margin: 0 auto;
        justify-content: center;
    }

    .container {
        padding: 14px;
    }

    .problem {
        margin: 20px auto;
        padding: 22px;
    }

    .options {
        gap: 14px;
        padding: 0 8px;
    }

    .navigation {
        gap: 12px;
        flex-wrap: wrap;
    }

    .scratchpad-area {
        width: 100%;
        min-height: auto;
        margin-top: 8px;
    }

    .scratchpad-canvas {
        height: 420px !important;
        min-height: 420px;
    }
}

@media (max-width: 768px) {
    body {
        padding: 14px;
        padding-bottom: calc(90px + env(safe-area-inset-bottom));
    }

    .main-content {
        margin-bottom: 68px;
    }

    .scratchpad-area {
        width: 100%;
        margin-top: 20px;
    }

    .options {
        grid-template-columns: 1fr;
    }

    .header-container {
        padding: 0 8px;
    }

    h1 {
        font-size: 24px;
        padding: 0;
    }

    .problem {
        padding: 20px;
    }

    .option {
        padding: 15px;
        min-height: var(--touch-target);
    }

    .navigation {
        flex-direction: column;
        align-items: stretch;
    }

    .nav-button {
        width: 100%;
        min-width: 0;
    }

    .home-button,
    .toggle-scratchpad,
    .scratchpad-button {
        width: 100%;
    }

    .scratchpad-controls {
        justify-content: stretch;
    }

    .home-page::before {
        background-size: 28px 28px;
    }
}

@media (max-width: 480px) {
    body {
        padding: 10px;
        padding-bottom: calc(88px + env(safe-area-inset-bottom));
    }

    .container {
        padding: 10px;
    }

    .problem {
        margin: 16px auto;
        padding: 16px;
        font-size: 1.1rem;
    }

    .options {
        margin: 20px auto;
        gap: 10px;
        padding: 0;
    }

    .scratchpad-canvas {
        height: 340px !important;
        min-height: 340px;
    }

    .scratchpad-button {
        padding: 10px 12px;
        font-size: 14px;
    }

    .flashcard-container {
        width: min(320px, 100%);
        height: 180px;
    }

    .flashcard-container.vertical {
        width: min(170px, 70vw);
        height: 300px;
    }

    .problem-type {
        font-size: 12px;
    }
}