:root {
    --bg-color: #121212;
    --text-color: #e0e0e0;
    --accent-color: #4CAF50;
    --panel-bg: #1e1e1e;
    --border-color: #333;
}

body {
    margin: 0;
    padding: 0;
    background-color: var(--bg-color);
    color: var(--text-color);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    display: flex;
    flex-direction: column;
    min-height: 100vh;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 15px 20px;
    background-color: var(--panel-bg);
    border-bottom: 1px solid var(--border-color);
    flex-wrap: wrap; /* flex fixes */
}

header h1 {
    margin: 0;
    font-size: 1.5rem;
}

.lang-selector button {
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-color);
    padding: 5px 10px;
    cursor: pointer;
    border-radius: 4px;
    margin-left: 5px;
}

.lang-selector button:hover {
    background: var(--border-color);
}

main {
    flex: 1;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.calculator {
    background-color: var(--panel-bg);
    padding: 30px;
    border-radius: 8px;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.3);
    width: 100%;
    max-width: 400px;
}

.form-group {
    margin-bottom: 20px;
}

.form-group label {
    display: block;
    margin-bottom: 8px;
}

select {
    width: 100%;
    padding: 10px;
    background-color: var(--bg-color);
    color: var(--text-color);
    border: 1px solid var(--border-color);
    border-radius: 4px;
    min-width: 0; /* min-width: 0 on inputs */
}

.results {
    margin: 30px 0;
    text-align: center;
}

#btn-simulate {
    width: 100%;
    padding: 15px;
    background-color: var(--accent-color);
    color: white;
    border: none;
    border-radius: 4px;
    font-size: 1.1rem;
    cursor: pointer;
    font-weight: bold;
}

#btn-simulate:hover {
    background-color: #45a049;
}

#btn-simulate:disabled {
    background-color: #555;
    color: #999;
    cursor: not-allowed;
}

#sim-status {
    text-align: center;
    margin-top: 10px;
    font-style: italic;
    color: #aaa;
}

footer {
    text-align: center;
    padding: 20px;
    background-color: var(--panel-bg);
    border-top: 1px solid var(--border-color);
}

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

footer a:hover {
    text-decoration: underline;
}