:root {
    --primary-color: #0d6efd;
    --secondary-color: #6c757d;
    --success-color: #198754;
    --danger-color: #dc3545;
    --warning-color: #ffc107;
    --light-color: #f8f9fa;
    --dark-color: #212529;
    --background-color: #e9ecef;
    --white-color: #fff;
    --font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    --box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
    --border-radius: 8px;
}

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

body {
    font-family: var(--font-family);
    background-color: var(--background-color);
    color: var(--dark-color);
    line-height: 1.6;
}

header {
    background-color: var(--dark-color);
    color: var(--white-color);
    padding: 1rem;
    text-align: center;
    box-shadow: 0 2px 5px rgba(0,0,0,0.2);
}

main {
    padding: 1.5rem;
    max-width: 1200px;
    margin: 0 auto;
    display: grid;
    gap: 1.5rem;
}

@media (min-width: 992px) {
    main {
        grid-template-columns: 1fr 1fr;
    }
    #units-list-container {
        grid-column: 1 / -1; /* Span across both columns */
    }
}

.container {
    background: var(--white-color);
    padding: 1.5rem;
    border-radius: var(--border-radius);
    box-shadow: var(--box-shadow);
}

h2, h3 {
    margin-bottom: 1rem;
    color: var(--primary-color);
    border-bottom: 2px solid var(--light-color);
    padding-bottom: 0.5rem;
}

form {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

input[type="text"],
input[type="number"],
input[type="url"],
input[type="file"],
textarea,
select {
    width: 100%;
    padding: 0.75rem;
    border: 1px solid #ccc;
    border-radius: var(--border-radius);
    font-size: 1rem;
    transition: border-color 0.2s;
}

input:focus, textarea:focus, select:focus {
    outline: none;
    border-color: var(--primary-color);
}

textarea {
    min-height: 120px;
    resize: vertical;
}

label {
    font-weight: 600;
    margin-bottom: -0.5rem;
}

button {
    padding: 0.8rem 1.5rem;
    font-size: 1rem;
    font-weight: 600;
    color: var(--white-color);
    background-color: var(--primary-color);
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    transition: background-color 0.2s, transform 0.2s;
}

button:hover {
    background-color: #0b5ed7;
    transform: translateY(-2px);
}

.message {
    padding: 1rem;
    margin-top: 1rem;
    border-radius: var(--border-radius);
    display: none;
    text-align: center;
    font-weight: 500;
}
.message.success {
    background-color: #d1e7dd;
    color: var(--success-color);
    display: block;
}
.message.error {
    background-color: #f8d7da;
    color: var(--danger-color);
    display: block;
}

.item-list {
    margin-top: 1rem;
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.item-card {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem;
    border: 1px solid #ddd;
    border-radius: var(--border-radius);
    background: var(--light-color);
}

.item-card-info {
    flex-grow: 1;
}

.item-card-actions {
    display: flex;
    gap: 0.5rem;
}

.edit-btn, .delete-btn {
    padding: 0.4rem 0.8rem;
    font-size: 0.9rem;
}
.edit-btn { background-color: var(--warning-color); color: var(--dark-color); }
.delete-btn { background-color: var(--danger-color); }

.hidden { display: none !important; }

/* Loader Styles */
#loader {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(255, 255, 255, 0.7);
    display: flex;
    justify-content: center;
    align-items: center;
    z-index: 1000;
}
.spinner {
    border: 8px solid #f3f3f3;
    border-top: 8px solid var(--primary-color);
    border-radius: 50%;
    width: 60px;
    height: 60px;
    animation: spin 1s linear infinite;
}
@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}