html {
    scrollbar-width: thin;
    scroll-behavior: smooth;
}

/* default theme */
:root {
    --bg-color: #121212;
    --card-bg: #1e1e1e;
    --text-main: #e0e0e0;
    --text-dim: #b0b0b0;
    --accent: #bb86fc;
    --border: #333;
    --nav-bg: rgba(18, 18, 18, 0.95);
    --speaker-bg: #1e1e1e;
    --th-bg: #252525;
    --button-bg: rgb(187, 134, 252, 0.7);
    --arrow-filter: invert(1);
}

/* light theme */
body.light-theme {
    --bg-color: #f4f4f9;
    --card-bg: #ffffff;
    --text-main: #1a1a1a;
    --text-dim: #555555;
    --accent: #7d3fd3;
    --border: #ddd;
    --nav-bg: rgba(244, 244, 249, 0.95);
    --th-bg: #eaeaeb;
    --button-bg: rgb(125, 63, 211, 0.7);
    --arrow-filter: invert(0);
}


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

body {
    font-family: "Bitcount Grid Single", system-ui;
    background-color: var(--bg-color);
    color: var(--text-main);
    line-height: 1.6;
    padding: 24px;
}

#theme-toggle {
    background: none;
    padding: 3px 10px;
    font-size: 1.1rem;
    right: 9;
    transition: all 0.3s ease;
}

#theme-toggle:hover {
    transform: scale(1.3);
}

header {
    text-align: center;
    padding: 4rem 1rem;
    border-bottom: 1px solid var(--border);

}

header h1 {
    font-size: 2.5rem;
    color: var(--accent);
    font-weight: 400;
}

.nav-logo {
    height: 70px;
    width: auto;
    transition: transform 0.1s ease;
}

.nav-logo:hover {
    transform: scale(1.1);
}

nav ul {
    display: flex;
    grid-template-columns: 1fr auto 1fr;
    justify-content: center;
    align-items: center;
    list-style: none;
    width: 100%;
    gap: 20px;
}


nav {
    position: -webkit-sticky;
    position: sticky;
    top: 0;
    background-color: var(--nav-bg);
    backdrop-filter: blur(10px);
    padding: 12px 0;
    z-index: 1000;
    border-bottom: 1px solid var(--border);
}

nav a {
    text-decoration: none;
    color: var(--text-dim);
    font-weight: 600;
    transition: color 0.3s;
}

nav a:hover {
    color: var(--accent);
}

.about h2 {
    font-weight: 400;
}

.about p {
    color: #bb86fc;
}

.schedule h2 {
    font-weight: 400;
}

.schedule th {
    font-weight: 500;
    font-size: medium;
}


main {
    max-width: 900px;
    margin: 0 auto;
}

section {
    padding: 46px 0;
    border-bottom: 1px solid var(--border);
}

.speakers h2 {
    font-weight: 400;
}

.speaker-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
    gap: 20px;
    margin-top: 20px;
}

.speaker-card {
    text-align: center;
    background: var(--th-bg);
    padding: 20px;
    border-radius: 8px;
    border: 1px solid #333;
    transition: transform 0.2s, border-color 0.2s;
}

.speaker-card :hover {
    transform: translateY(-1px);
    border-color: var(--accent);
}

.speaker-card img {
    width: 120px;
    height: 150px;
    border-radius: 12px;
    border: 2px solid var(--border);
    object-fit: cover;
}

.speaker-card h3 {
    color: var(--accent);
    margin-bottom: 5px;
    font-size: 1.2rem;
    font-weight: 500;
}

.speaker-card p {
    color: #929191;
    font-size: 0.9rem;
    font-style: italic;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 20px;
    background: var(--card-bg);
    border-radius: 8px;
    overflow: hidden;
}

th,
td {
    padding: 12px;
    text-align: left;
    border-bottom: 1px solid var(--border);
}

th {
    background-color: var(--th-bg);
    color: var(--accent);
    text-transform: uppercase;
    font-size: 0.9rem;
    letter-spacing: 2px;
}

form {
    display: flex;
    flex-direction: column;
    max-width: 100%;
    gap: 12px;
}

input,
textarea {
    background: var(--card-bg);
    border: 1px solid var(--border);
    padding: 12px;
    color: rgb(117, 116, 116);
    border-radius: 4px;
}


button {
    background: var(--button-bg);
    color: black;
    padding: 12px;
    border: none;
    border-radius: 4px;
    font-weight: bold;
    cursor: pointer;
    transition: opacity 0.3s;
}

button:hover {
    opacity: 0.8;
}

:focus-visible {
    outline: 2px dashed var(--accent);
    outline-offset: 4px;
}

a:focus-visible,
button:focus-visible {
    outline: 2px dashed var(--accent);
    border-radius: 4px;
}

:focus:not(:focus-visible) {
    outline: none;
}

.contact h2 {
    font-weight: 400;
}


#backToTop {
    display: none;
    position: fixed;
    bottom: 30px;
    right: 30px;
    width: 140px;
    height: auto;
    z-index: 1000;
    background: none;
    padding: 0;
    border: none;
    cursor: pointer;
    transition: transform 0.1 ease;
}

#backToTop img {
    max-width: 100%;
    max-height: auto;
    object-fit: contain;
    mix-blend-mode: lighten;
    filter: var(--arrow-filter);
}

#backToTop :hover {
    transform: scale(1.2);
}

@keyframes bounce {

    0%,
    100% {
        transform: translateY(0);
    }

    50% {
        transform: translateY(-5px);
    }
}

#backToTop:hover img {
    animation: bounce 1s infinite;
}

.modal {
    display: none;
    position: fixed;
    z-index: 2000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.8);
    backdrop-filter: blur(5px);
}

.modal-content h2 {
    font-weight: 400;
    font-size: xx-large;
}

.modal-content {
    background-color: var(--card-bg);
    margin: 15% auto;
    padding: 22px;
    border: 1px solid var(--accent);
    border-radius: 20px;
    width: 90%;
    text-align: center;
    position: relative;
    animation: modalFadeIn 0.4s ease;
}

.modal-icon {
    font-size: 3rem;
    color: var(--accent);
    margin-bottom: 12px;
}

#modalCloseBtn {
    margin-top: 24px;
    width: 50%;
}

button,
input,
select,
textarea {
    font-family: inherit;
    font-size: inherit;
}