:root {
    --bg-color: #f4f4f4;
    --card-bg-color: #ffffff;
    --text-color: #333;
    --heading-color: #2c3e50;
    --border-color: #ddd;
    --shadow-color: rgba(0,0,0,0.1);
    --tag-bg-color: #e0e0e0;
    --button-bg: #3498db;
    --button-hover: #2980b9;
    --control-bg: #ffffff;
    --control-border: #ccc;
    --status-ongoing: #2ecc71;
    --status-countdown: #e74c3c;
    --status-ended: #95a5a6;
}

body.dark-mode {
    --bg-color: #121212;
    --card-bg-color: #1e1e1e;
    --text-color: #e0e0e0;
    --heading-color: #e0e0e0;
    --border-color: #444;
    --shadow-color: rgba(0,0,0,0.4);
    --tag-bg-color: #333;
    --button-bg: #3498db;
    --button-hover: #5dade2;
    --control-bg: #1e1e1e;
    --control-border: #555;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    line-height: 1.6;
    background-color: var(--bg-color);
    color: var(--text-color);
    margin: 0;
    padding: 20px;
    transition: background-color 0.3s, color 0.3s;
}

h1 {
    text-align: center;
    color: var(--heading-color);
}

.section-header {
    font-size: 1.8em;
    font-weight: 600;
    color: var(--heading-color);
    margin-top: 40px;
    margin-bottom: 10px;
    padding-bottom: 5px;
    border-bottom: 2px solid var(--button-bg);
}

.controls-container {
    max-width: 1000px;
    margin: 20px auto;
    padding: 15px;
    background-color: var(--control-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    box-shadow: 0 2px 4px var(--shadow-color);
    display: flex;
    flex-wrap: wrap;
    gap: 20px;
    align-items: center;
}

.control-group {
    display: flex;
    align-items: center;
    gap: 8px;
}
.control-group.toggles {
    margin-left: auto;
}

.control-group label {
    font-weight: 500;
}

.control-group input[type="text"],
.control-group select,
.control-group button {
    padding: 8px 12px;
    border: 1px solid var(--control-border);
    background-color: var(--card-bg-color); 
    color: var(--text-color);
    border-radius: 4px;
    font-size: 14px;
}

.control-group input[type="text"] {
    min-width: 250px;
}

.control-group button {
    background-color: var(--button-bg);
    color: white;
    border: none;
    cursor: pointer;
    transition: background-color 0.2s;
}

.control-group button:hover {
    background-color: var(--button-hover);
}

#theme-toggle {
    min-width: 40px;
    text-align: center;
}


#countdown-container {
    max-width: 1000px;
    margin: 20px auto;
    padding: 10px;
    transition: grid-template-columns 0.3s ease;
}


#countdown-container.single-column {}

#countdown-container.double-column {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 20px;
}


.conference-card {
    background-color: var(--card-bg-color);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    padding: 20px;
    margin-bottom: 20px;
    box-shadow: 0 2px 4px var(--shadow-color);
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    transition: background-color 0.3s, border-color 0.3s;
}

.conference-card h2 {
    margin-top: 0;
    color: var(--button-bg); 
    font-size: 1.5em;
}

.conference-card h2 a {
    text-decoration: none;
    color: inherit;
}

.conference-card p {
    margin-bottom: 5px;
}


.tags {
    margin: 10px 0;
}
.tag {
    display: inline-block;
    padding: 4px 10px;
    border-radius: 12px;
    font-size: 0.9em;
    font-weight: 500;
    margin-right: 8px;
}
.tag-rank {
    background-color: #f1c40f;
    color: #5d4a00;
}
.tag-sub {
    background-color: var(--tag-bg-color);
    color: var(--text-color);
}


.countdown-status {
    font-size: 1.3em;
    font-weight: bold;
    margin-top: 10px;
}
.status-countdown {
    color: var(--status-countdown);
}
.status-ongoing {
    color: var(--status-ongoing);
}
.status-ended {
    color: var(--status-ended);
}


#scroll-to-top {
    position: fixed;
    bottom: 20px;
    right: 20px;
    width: 40px;
    height: 40px;
    background-color: var(--button-bg);
    color: white;
    border: none;
    border-radius: 50%;
    font-size: 20px;
    line-height: 40px;
    text-align: center;
    cursor: pointer;
    opacity: 0; 
    visibility: hidden;
    transition: opacity 0.3s, visibility 0.3s, background-color 0.3s;
    z-index: 1000;
}
#scroll-to-top:hover {
    background-color: var(--button-hover);
}
#scroll-to-top.show {
    opacity: 1;
    visibility: visible;
}

@media (max-width: 1024px) {
    .control-group input[type="text"] {
        min-width: 200px;
    }
}

@media (max-width: 768px) {
    #countdown-container.double-column {
        grid-template-columns: 1fr;
    }
    
    .controls-container {
        flex-direction: column;
        align-items: stretch;
    }
    .control-group input[type="text"] {
        min-width: auto;
        width: 100%;
        box-sizing: border-box;
    }
    .control-group {
        width: 100%;
    }
    .control-group.toggles {
        margin-left: 0;
        flex-direction: row;
        justify-content: space-between;
    }
    .control-group.toggles button {
        width: 48%; 
    }
}