:root{--primary-color: #007bff;--secondary-color: #6c757d;--danger-color: #dc3545;--light-color: #e0e0e0;--dark-color: #343a40;--background-color: #f0f0f0;--button-hover-color: #d0d0d0;--button-transition: background-color .3s ease-out;--shadow-color: rgba(0, 0, 0, .2)}[data-theme=dark]{--primary-color: #1857ad;--secondary-color: #333;--danger-color: #b02f2f;--light-color: #666;--dark-color: #ccc;--background-color: #222;--button-hover-color: #555;--shadow-color: rgba(100, 100, 100, .2)}body{display:flex;justify-content:center;align-items:center;height:100vh;background-color:var(--background-color);margin:0;font-family:Arial,sans-serif}#theme-toggle{position:absolute;top:10px;right:10px;background:none;border:none;font-size:1.5em;cursor:pointer;transition:transform .3s}#theme-toggle:hover{transform:scale(1.2)}.calculator{background-color:var(--background-color);padding:20px;border-radius:10px;box-shadow:0 0 10px var(--shadow-color)}.display{margin-bottom:20px;color:var(--dark-color)}#result{width:100%;padding:10px;font-size:2em;text-align:right;border:none;background-color:var(--light-color);border-radius:5px;box-sizing:border-box;color:var(--dark-color)}.buttons{display:grid;grid-template-columns:repeat(4,1fr);gap:10px}.btn{color:var(--dark-color);padding:20px;font-size:1.5em;border:none;border-radius:5px;background-color:var(--light-color);cursor:pointer;transition:var(--button-transition)}.btn:hover{background-color:var(--button-hover-color)}.btn.mod{background-color:var(--secondary-color);color:#fff}.btn.mod:hover{background-color:var(--dark-color)}.btn.enter{background-color:var(--primary-color);color:#fff}.btn.enter:hover{background-color:var(--dark-color)}.btn.clear{background-color:var(--danger-color);color:#fff}.btn.clear:hover{background-color:var(--dark-color)}.btn.plus{background-color:var(--secondary-color);color:#fff}.btn.plus:hover{background-color:var(--dark-color)}.error-glow{border:2px solid var(--danger-color);box-shadow:0 0 8px var(--danger-color);transition:box-shadow .3s ease,border-color .3s ease,transform .2s ease-in-out,opacity .3s ease;transform:scale(1);opacity:1}.glow{border:2px solid var(--primary-color);box-shadow:0 0 8px var(--primary-color);transition:box-shadow .3s ease,border-color .3s ease,transform .2s ease-in-out,opacity .3s ease;transform:scale(1);opacity:1}#history-section{width:30%;overflow-y:auto;box-shadow:-3px 0 8px var(--shadow-color);padding:15px;background:var(--background-color);font-family:Arial,sans-serif;border-radius:10px}#clear-history{display:block;width:95%;background-color:var(--danger-color);color:#fff;font-size:14px;font-weight:700;padding:12px 8px;margin-bottom:15px;border:none;border-radius:8px;cursor:pointer;box-shadow:0 2px 6px var(--shadow-color);transition:var(--button-transition);outline:none}#clear-history:hover{background:#ff3535}#history-list{list-style:none;padding:0;margin:0;max-height:400px;overflow-y:auto;scrollbar-width:thin;scrollbar-color:var(--light-color) var(--background-color);border-radius:10px}.history-item{display:flex;width:80%;justify-content:space-between;align-items:center;background-color:var(--light-color);color:var(--dark-color);border:0;border-radius:8px;padding:10px 15px;margin:8px 0;font-size:.9em;position:relative;transition:var(--button-transition)}.history-item:hover{background-color:var(--button-hover-color)}.delete-btn{opacity:0;font-size:18px;color:var(--danger-color);cursor:pointer;margin-left:10px;transition:opacity .2s ease,transform .2s ease,color .2s ease;background-color:transparent}.history-item:hover .delete-btn{display:inline;color:var(--danger-color);opacity:1}.delete-btn:hover{transform:scale(1.2);color:var(--dark-color)}.calculator-container{display:flex;gap:20px;width:50%;max-width:800px;border-radius:15px;overflow:hidden;box-shadow:0 0 10px var(--shadow-color);padding:20px;background-color:var(--background-color)}.calculator{flex:65%}#history-section{flex:35%}