:root {
    --radius: 6px;
    --transition: 0.15s ease;
}

*, *::before, *::after {
    box-sizing: border-box;
}

::selection {
    background: var(--accent);
    color: var(--crust);
}

body {
    font-family: ui-monospace, 'Cascadia Code', 'Source Code Pro', Menlo, Consolas, monospace;
    max-width: 800px;
    margin: 40px auto;
    padding: 0 20px;
    background: var(--bg);
    color: var(--text);
    line-height: 1.6;
}

h1, h2, h3 {
    color: var(--text);
    margin-top: 1.5em;
    margin-bottom: 0.5em;
    line-height: 1.2;
}

h1 {
    border-bottom: 1px solid var(--surface-2);
    padding-bottom: 10px;
}

a {
    color: var(--accent);
    text-decoration: none;
    transition: opacity var(--transition);
}

a:hover {
    text-decoration: underline;
}

nav {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 14px;
    border-bottom: 1px dashed var(--surface-2);
    padding-bottom: 16px;
    margin-bottom: 32px;
}

.nav-controls {
    display: flex;
    align-items: center;
    flex-wrap: wrap;
    gap: 16px;
}

.nav-item {
    display: flex;
    align-items: center;
    gap: 8px;
}

.nav-label {
    font-size: 0.85rem;
    color: var(--surface-2);
}

.star-counter {
    color: var(--success);
    font-weight: bold;
    font-size: 0.95rem;
    letter-spacing: 1px;
}

pre {
    background: var(--crust);
    padding: 14px 16px;
    border: 1px solid var(--surface-2);
    border-radius: var(--radius);
    overflow-x: auto;
    width: fit-content;
    max-width: 100%;
    margin: 16px 0;
}

pre code {
    background: transparent;
    padding: 0;
    border: none;
}

code {
    background: var(--surface-0);
    padding: 2px 6px;
    border: 1px solid var(--surface-1);
    border-radius: var(--radius);
    font-size: 0.9em;
    word-break: break-word;
}

ul, ol {
    list-style: none;
    padding: 0;
    margin: 16px 0;
}

ol {
    counter-reset: list-counter;
}

ul > li, ol > li {
    position: relative;
    padding-left: 28px;
    margin-bottom: 10px;
    line-height: 1.6;
}

ul > li::before {
    content: "-";
    position: absolute;
    left: 2px;
    color: var(--accent);
    font-weight: bold;
}

ol > li::before {
    counter-increment: list-counter;
    content: counter(list-counter) ".";
    position: absolute;
    left: 2px;
    color: var(--accent);
    font-weight: bold;
    font-family: inherit;
}

input, button, select {
    font-family: inherit;
    font-size: 0.9rem;
    padding: 8px 12px;
    background: var(--crust);
    color: var(--text);
    border: 1px solid var(--surface-2);
    border-radius: var(--radius);
    transition: border-color var(--transition), background var(--transition);
    max-width: 100%;
}

input:hover, button:hover, select:hover {
    border-color: var(--accent);
}

input:focus-visible, button:focus-visible, select:focus-visible {
    outline: 2px solid var(--accent);
    outline-offset: 2px;
}

button {
    cursor: pointer;
    color: var(--accent);
    white-space: normal;
    text-align: center;
}

button:hover {
    background: var(--surface-0);
}

button:active {
    transform: translateY(1px);
}

select {
    appearance: none;
    -webkit-appearance: none;
    -moz-appearance: none;
    padding-right: 28px;
    cursor: pointer;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='10' height='6' viewBox='0 0 10 6'%3E%3Cpath fill='%23a6adc8' d='M0 0l5 6 5-6z'/%3E%3C/svg%3E");
    background-repeat: no-repeat;
    background-position: right 10px center;
}

select optgroup {
    background-color: var(--crust);
    color: var(--accent);
    font-weight: bold;
}

select option {
    background: var(--crust);
    color: var(--text);
}

input[type="number"]::-webkit-inner-spin-button,
input[type="number"]::-webkit-outer-spin-button {
    -webkit-appearance: none;
    margin: 0;
}
input[type="number"] {
    -moz-appearance: textfield;
}

.challenge-divider {
    border: none;
    border-top: 1px dashed var(--surface-2);
    margin: 48px 0 24px;
}

.challenge-actions {
    display: flex;
    flex-direction: column;
    gap: 16px;
    background: var(--surface-0);
    padding: 20px;
    border: 1px solid var(--surface-1);
    border-radius: var(--radius);
}

#challenge-input {
    margin: 0;
    width: 100%;
    color: var(--surface-2);
}

.answer-form {
    display: flex;
    align-items: center;
    gap: 8px;
    flex-wrap: wrap;
    margin-top: 0;
}

.answer-form input {
    width: 200px;
    font-size: 1rem;
}

#result-msg {
    font-size: 0.95rem;
    margin-left: 4px;
}

#result-msg:empty {
    display: none;
}

.success { color: var(--success); font-weight: bold; }
.fail    { color: var(--error);   font-weight: bold; }

.calendar-month {
    margin-bottom: 48px;
}

.month-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--surface-2);
    padding-bottom: 10px;
    margin-bottom: 20px;
    margin-top: 32px;
}

.month-header h2 {
    margin: 0;
    font-size: 1.35rem;
}

.month-overview-link {
    font-size: 0.88rem;
}

.calendar-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(130px, 1fr));
    gap: 14px;
}

.calendar-card {
    background: var(--surface-0);
    border: 1px solid var(--surface-1);
    border-radius: var(--radius);
    padding: 14px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    min-height: 110px;
    text-decoration: none;
    transition: transform var(--transition), border-color var(--transition), background-color var(--transition);
}

.calendar-card:hover {
    border-color: var(--accent);
    background-color: var(--crust);
    transform: translateY(-2px);
    text-decoration: none;
}

.calendar-card.solved {
    border-color: var(--success);
}

.calendar-card.solved .calendar-star {
    color: var(--success);
    text-shadow: 0 0 8px var(--success);
}

.calendar-card-header {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
}

.calendar-day-num {
    font-size: 1.6rem;
    font-weight: bold;
    color: var(--accent);
    line-height: 1;
}

.calendar-star {
    font-size: 0.9rem;
    color: var(--surface-2);
    transition: color var(--transition);
}

.calendar-card:hover .calendar-star {
    color: var(--accent);
}

.calendar-day-title {
    font-size: 0.85rem;
    color: var(--text);
    margin-top: 10px;
    line-height: 1.3;
}

.calendar-card.locked {
    opacity: 0.45;
    cursor: not-allowed;
    background: var(--crust);
    border-style: dashed;
}

.calendar-card.locked:hover {
    transform: none;
    border-color: var(--surface-1);
}

.calendar-card.locked .calendar-day-num {
    color: var(--surface-2);
}

.calendar-lock {
    font-size: 0.85rem;
}

::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}
::-webkit-scrollbar-track {
    background: var(--crust);
}
::-webkit-scrollbar-thumb {
    background: var(--surface-1);
    border-radius: var(--radius);
}
::-webkit-scrollbar-thumb:hover {
    background: var(--surface-2);
}

@media (max-width: 640px) {
    body {
        margin: 20px auto;
        padding: 0 16px;
    }

    nav {
        flex-direction: column;
        align-items: flex-start;
        gap: 16px;
    }

    .nav-controls {
        width: 100%;
        justify-content: space-between;
        gap: 12px;
    }

    .nav-item {
        flex-direction: column;
        align-items: flex-start;
        gap: 6px;
        width: 100%;
    }

    .nav-item select,
    .nav-item input {
        width: 100% !important;
    }

    pre {
        width: 100%;
    }

    .challenge-actions {
        padding: 16px;
    }

    .answer-form input {
        width: 100%;
    }

    .answer-form button {
        width: 100%;
    }

    input, button, select {
        padding: 10px 12px;
    }
}