:root {
    --primary-color: #4A90E2;
    --primary-dark: #357ABD;
    --background-color: #F5F7FA;
    --surface-color: #FFFFFF;
    --text-main: #333333;
    --text-sub: #666666;
    --saturday-color: #3B82F6; /* Modern Blue */
    --sunday-color: #EF4444;   /* Modern Red */
    --weekday-color: #1F2937;
    --border-color: #E5E7EB;
    --header-bg: rgba(255, 255, 255, 0.9);
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --radius-lg: 12px;
    --radius-md: 8px;
}

* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    -webkit-tap-highlight-color: transparent;
}

body {
    font-family: 'Roboto', 'Noto Sans JP', sans-serif;
    background-color: var(--background-color);
    color: var(--text-main);
    line-height: 1.5;
    -webkit-font-smoothing: antialiased;
}

.app-container {
    max-width: 600px;
    margin: 0 auto;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    background-color: var(--surface-color);
    box-shadow: 0 0 20px rgba(0,0,0,0.03);
}

/* Header */
.app-header {
    background-color: var(--header-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    padding: 1rem;
    position: sticky;
    top: 0;
    z-index: 100;
    border-bottom: 1px solid var(--border-color);
    text-align: center;
}

.app-header h1 {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--text-main);
    margin: 0;
}

/* Main Content */
.main-content {
    flex: 1;
    padding: 1.5rem;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
}

/* Input Area */
.input-area {
    background: var(--surface-color);
    border-radius: var(--radius-lg);
    display: flex;
    flex-direction: column;
    gap: 1.25rem;
}

.date-selector {
    display: flex;
    justify-content: center;
    gap: 1rem;
    align-items: center;
}

.select-wrapper {
    position: relative;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

select {
    appearance: none;
    -webkit-appearance: none;
    background-color: #fff;
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    padding: 0.75rem 1rem;
    font-size: 1.2rem;
    font-weight: 500;
    min-width: 80px;
    text-align: center;
    color: var(--text-main);
    cursor: pointer;
    box-shadow: var(--shadow-sm);
    transition: border-color 0.2s, box-shadow 0.2s;
}

select:focus {
    outline: none;
    border-color: var(--primary-color);
    box-shadow: 0 0 0 3px rgba(74, 144, 226, 0.2);
}

.unit {
    font-weight: 700;
    font-size: 1rem;
    color: var(--text-sub);
}

.calc-btn {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    color: white;
    border: none;
    padding: 1rem;
    border-radius: var(--radius-md);
    font-size: 1.1rem;
    font-weight: 700;
    cursor: pointer;
    box-shadow: var(--shadow-md);
    transition: transform 0.1s, box-shadow 0.1s;
    width: 100%;
    min-height: 54px; /* Ensure easy tapping */
}

.calc-btn:active {
    transform: translateY(1px);
    box-shadow: var(--shadow-sm);
}

/* Result Area */
.result-area {
    display: flex;
    flex-direction: column;
}

.result-header {
    display: flex;
    justify-content: space-between;
    padding: 0.75rem 1.5rem;
    font-weight: 700;
    color: var(--text-sub);
    border-bottom: 2px solid var(--border-color);
    margin-bottom: 0.5rem;
}

.result-list {
    list-style: none;
    padding-bottom: 2rem;
}

.result-list li {
    display: flex;
    justify-content: space-between;
    padding: 1rem 1.5rem;
    border-bottom: 1px solid var(--border-color);
    font-size: 1.1rem;
    animation: fadeIn 0.3s ease-out forwards;
    opacity: 0;
}

/* Staggered animation effect for the first few items can be done via JS or just simple fade in */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Coloring */
.weekday-sat {
    color: var(--saturday-color);
    font-weight: 700;
}

.weekday-sun {
    color: var(--sunday-color);
    font-weight: 700;
}

.weekday-normal {
    color: var(--weekday-color);
}

.invalid-date {
    color: #9CA3AF;
    font-style: italic;
}

/* Stripes for readability */
.result-list li:nth-child(even) {
    background-color: #F9FAFB;
}