:root {
    --bg: #e0e0e0;
    --calc-bg: linear-gradient(145deg, #ffffff, #e6e6e6);
    --text: #333;
    --shadow1: #bebebe;
    --shadow2: #ffffff;
    --accent-green: #27ae60;
    --accent-blue: #3498db;
    --accent-red: #e74c3c;
    --screen-bg: inset 6px 6px 12px #c4c4c4, inset -6px -6px 12px #ffffff;
}

[data-theme="dark"] {
    --bg: #1a1a1a;
    --calc-bg: linear-gradient(145deg, #1e1e1e, #171717);
    --text: #e0e0e0;
    --shadow1: #0d0d0d;
    --shadow2: #262626;
    --screen-bg: inset 6px 6px 12px #0a0a0a, inset -6px -6px 12px #2a2a2a;
}

* { margin: 0; padding: 0; box-sizing: border-box; transition: all 0.3s ease; }

body { 
    background: var(--bg); 
    display: flex; 
    justify-content: center; 
    align-items: center; 
    min-height: 100vh; 
    font-family: 'Segoe UI', system-ui, sans-serif; 
    padding: 20px;
    color: var(--text);
}

.container { display: flex; flex-direction: column; align-items: center; gap: 20px; width: 100%; max-width: 420px; }

/* Controles Superiores */
.top-controls {
    display: flex;
    justify-content: space-between;
    width: 100%;
    padding: 0 10px;
}

.mode-btn {
    padding: 8px 18px;
    border-radius: 20px;
    border: none;
    background: var(--calc-bg);
    box-shadow: 4px 4px 8px var(--shadow1), -4px -4px 8px var(--shadow2);
    cursor: pointer;
    font-size: 12px;
    font-weight: bold;
    color: var(--text);
}

.mode-btn:active { box-shadow: inset 3px 3px 6px var(--shadow1), inset -3px -3px 6px var(--shadow2); }

/* Calculadora */
.calc { 
    background: var(--calc-bg); 
    padding: 25px; 
    border-radius: 35px; 
    box-shadow: 20px 20px 60px var(--shadow1), -20px -20px 60px var(--shadow2); 
    width: 100%;
}

/* Pantalla */
.screen {
    background: var(--bg);
    border-radius: 15px;
    padding: 15px;
    box-shadow: var(--screen-bg);
    margin-bottom: 20px;
    border: 2px solid rgba(0,0,0,0.05);
}

.info-panel {
    display: flex;
    justify-content: space-between;
    font-size: 11px;
    opacity: 0.7;
    margin-bottom: 8px;
    font-weight: bold;
    font-family: monospace;
}

.expression { 
    font-size: 15px; 
    color: var(--accent-blue); 
    text-align: right; 
    min-height: 20px; 
    font-family: 'Share Tech Mono', monospace;
    opacity: 0.8;
    letter-spacing: 1px;
}

#display { 
    width: 100%; 
    border: none; 
    background: transparent;
    text-align: right; 
    font-size: 34px; 
    color: var(--text); 
    outline: none;
    font-family: 'Share Tech Mono', monospace;
    letter-spacing: 2px;
}

/* Botones unificados */
.buttons { display: grid; grid-template-columns: repeat(4, 1fr); gap: 10px; }

.btn { 
    height: 50px; 
    border-radius: 12px; 
    border: none; 
    background: var(--calc-bg); 
    box-shadow: 4px 4px 8px var(--shadow1), -4px -4px 8px var(--shadow2); 
    cursor: pointer; 
    font-size: 16px; 
    font-weight: 600; 
    color: var(--text);
    display: flex; align-items: center; justify-content: center;
}

.btn:active { box-shadow: inset 3px 3px 6px var(--shadow1), inset -3px -3px 6px var(--shadow2); transform: scale(0.95); }

.btn-op { color: #d35400; font-size: 18px; }
.btn-func { color: var(--accent-blue); font-size: 13px; }
.btn-mem { color: #8e44ad; font-size: 14px; }
.btn-clear { background: var(--accent-red); color: white; }

/* Modificación para que el igual ocupe 4 columnas */
.btn-eq { 
    grid-column: span 4; 
    background: var(--accent-green); 
    color: white; 
    font-size: 24px; 
    height: 55px; /* Ligeramente más alto para destacar */
}

/* Historial */
.history-panel {
    width: 100%;
    max-height: 90px;
    overflow-y: auto;
    font-size: 13px;
    margin-top: 15px;
    padding: 10px;
    border-radius: 10px;
    background: rgba(0,0,0,0.05);
    text-align: right;
    font-family: 'Share Tech Mono', monospace;
}

.history-panel p { margin-bottom: 5px; opacity: 0.7; border-bottom: 1px solid rgba(0,0,0,0.05); padding-bottom: 3px;}

/* Branding Footer */
.footer { 
    text-align: center; 
    background: var(--calc-bg); 
    padding: 20px; 
    border-radius: 25px; 
    box-shadow: 10px 10px 30px var(--shadow1), -10px -10px 30px var(--shadow2); 
    width: 100%; 
}

.footer h3 { margin-bottom: 15px; font-size: 15px; color: var(--accent-blue); font-weight: bold;}

.social-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 12px;
}

.footer a { 
    text-decoration: none; 
    color: var(--text); 
    font-size: 12px; 
    display: flex; 
    align-items: center; 
    gap: 8px; 
    padding: 10px;
    border-radius: 12px;
    background: var(--bg);
    box-shadow: 3px 3px 6px var(--shadow1), -3px -3px 6px var(--shadow2);
    font-weight: 500;
}

.footer a:hover { transform: translateY(-3px); color: var(--accent-blue); }

/* Estilo especial para destacar YouTube */
.youtube-btn {
    grid-column: span 2;
    justify-content: center;
    font-size: 14px !important;
}

@media (max-width: 400px) {
    .buttons { gap: 8px; }
    .btn { height: 45px; font-size: 14px; }
    #display { font-size: 28px; }
}