diff --git a/api/controller.js b/api/controller.js
index 949731c..b43da2d 100644
--- a/api/controller.js
+++ b/api/controller.js
@@ -16,6 +16,12 @@ exports.calculate = function(req, res) {
     'subtract': function(a, b) { return a - b },
     'multiply': function(a, b) { return a * b },
     'divide':   function(a, b) { return a / b },
+    'sin':      function(a) { return Math.sin(a) },
+    'cos':      function(a) { return Math.cos(a) },
+    'tan':      function(a) { return Math.tan(a) },
+    'sqrt':     function(a) { return Math.sqrt(a) },
+    'power':    function(a, b) { return Math.pow(a, b) },
+    'log':      function(a) { return Math.log10(a) },
   };
 
   if (!req.query.operation) {
@@ -29,16 +35,23 @@ exports.calculate = function(req, res) {
   }
 
   if (!req.query.operand1 ||
-      !req.query.operand1.match(/^(-)?[0-9\.]+(e(-)?[0-9]+)?$/) ||
+      !req.query.operand1.match(/^(-)?[0-9.]+(e(-)?[0-9]+)?$/) ||
       req.query.operand1.replace(/[-0-9e]/g, '').length > 1) {
     throw new Error("Invalid operand1: " + req.query.operand1);
   }
 
-  if (!req.query.operand2 ||
-      !req.query.operand2.match(/^(-)?[0-9\.]+(e(-)?[0-9]+)?$/) ||
-      req.query.operand2.replace(/[-0-9e]/g, '').length > 1) {
-    throw new Error("Invalid operand2: " + req.query.operand2);
-  }
+  // Check if operation requires two operands
+  var singleOperandOps = ['sin', 'cos', 'tan', 'sqrt', 'log'];
+  var requiresTwoOperands = singleOperandOps.indexOf(req.query.operation) === -1;
 
-  res.json({ result: operation(req.query.operand1, req.query.operand2) });
+  if (requiresTwoOperands) {
+    if (!req.query.operand2 ||
+        !req.query.operand2.match(/^(-)?[0-9.]+(e(-)?[0-9]+)?$/) ||
+        req.query.operand2.replace(/[-0-9e]/g, '').length > 1) {
+      throw new Error("Invalid operand2: " + req.query.operand2);
+    }
+    res.json({ result: operation(req.query.operand1, req.query.operand2) });
+  } else {
+    res.json({ result: operation(req.query.operand1) });
+  }
 };
diff --git a/public/client.js b/public/client.js
index 1d21fd9..7c301b0 100644
--- a/public/client.js
+++ b/public/client.js
@@ -33,13 +33,28 @@ function calculate(operand1, operand2, operation) {
         case '/':
             uri += "?operation=divide";
             break;
+        case 'power':
+            uri += "?operation=power";
+            break;
+        case 'sin':
+        case 'cos':
+        case 'tan':
+        case 'sqrt':
+        case 'log':
+            uri += "?operation=" + operation;
+            break;
         default:
             setError();
             return;
     }
 
     uri += "&operand1=" + encodeURIComponent(operand1);
-    uri += "&operand2=" + encodeURIComponent(operand2);
+    
+    // Only add operand2 for operations that need it
+    var singleOperandOps = ['sin', 'cos', 'tan', 'sqrt', 'log'];
+    if (singleOperandOps.indexOf(operation) === -1) {
+        uri += "&operand2=" + encodeURIComponent(operand2);
+    }
 
     setLoading(true);
 
@@ -132,6 +147,44 @@ function equalPressed() {
     calculate(operand1, operand2, operation);
 }
 
+function scientificOperation(op) {
+    // Scientific operations work on the current value immediately
+    var currentValue = getValue();
+    
+    // Save state for potential chaining
+    operand1 = currentValue;
+    operation = op;
+    state = states.complete;
+    
+    // Calculate immediately (operand2 not needed for these operations)
+    calculate(currentValue, null, op);
+}
+
+function toggleTheme() {
+    var body = document.body;
+    var themeIcon = document.querySelector('.theme-icon');
+    
+    if (body.classList.contains('dark-theme')) {
+        body.classList.remove('dark-theme');
+        body.classList.add('light-theme');
+        themeIcon.textContent = '🌙';
+    } else if (body.classList.contains('light-theme')) {
+        body.classList.remove('light-theme');
+        body.classList.add('dark-theme');
+        themeIcon.textContent = '☀️';
+    } else {
+        // First time toggle - check system preference
+        var prefersDark = window.matchMedia('(prefers-color-scheme: dark)').matches;
+        if (prefersDark) {
+            body.classList.add('light-theme');
+            themeIcon.textContent = '🌙';
+        } else {
+            body.classList.add('dark-theme');
+            themeIcon.textContent = '☀️';
+        }
+    }
+}
+
 // Enhanced keyboard support
 document.addEventListener('keydown', (event) => {
     // Handle keydown for special keys
diff --git a/public/default.css b/public/default.css
index bd14feb..d91f51e 100644
--- a/public/default.css
+++ b/public/default.css
@@ -10,6 +10,9 @@
     --button-operator: #007bff;
     --button-operator-hover: #0056b3;
     --button-operator-active: #004085;
+    --button-scientific: #6f42c1;
+    --button-scientific-hover: #5a32a3;
+    --button-scientific-active: #4c2a8a;
     --button-equals: #28a745;
     --button-equals-hover: #1e7e34;
     --button-equals-active: #155724;
@@ -42,6 +45,32 @@
     }
 }
 
+/* Light theme override */
+body.light-theme {
+    --primary-bg: #f0f2f5;
+    --calculator-bg: #ffffff;
+    --display-bg: #1e1e1e;
+    --display-text: #ffffff;
+    --button-bg: #f8f9fa;
+    --button-hover: #e9ecef;
+    --button-active: #dee2e6;
+    --text-primary: #212529;
+    --text-secondary: #6c757d;
+}
+
+/* Dark theme override */
+body.dark-theme {
+    --primary-bg: #121212;
+    --calculator-bg: #1e1e1e;
+    --display-bg: #000000;
+    --display-text: #ffffff;
+    --button-bg: #2d2d2d;
+    --button-hover: #3d3d3d;
+    --button-active: #4d4d4d;
+    --text-primary: #ffffff;
+    --text-secondary: #adb5bd;
+}
+
 BODY {
     height: 100vh;
     width: 100vw;
@@ -108,6 +137,36 @@ BODY {
     min-height: auto;
 }
 
+/* Theme toggle button */
+.theme-toggle {
+    position: absolute;
+    top: 1rem;
+    right: 1rem;
+    background: var(--button-bg);
+    border: none;
+    border-radius: 50%;
+    width: 50px;
+    height: 50px;
+    font-size: 1.5rem;
+    cursor: pointer;
+    box-shadow: var(--shadow-md);
+    transition: all var(--transition-duration) ease;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 100;
+}
+
+.theme-toggle:hover {
+    background: var(--button-hover);
+    transform: scale(1.1);
+    box-shadow: var(--shadow-lg);
+}
+
+.theme-toggle:active {
+    transform: scale(0.95);
+}
+
 #results {
     margin-bottom: 1.5rem;
     width: 100%;
@@ -266,6 +325,21 @@ BODY {
     background: var(--button-clear-active);
 }
 
+/* Scientific button styling */
+.btn-scientific {
+    background: var(--button-scientific);
+    color: white;
+    font-size: 1rem;
+}
+
+.btn-scientific:hover {
+    background: var(--button-scientific-hover);
+}
+
+.btn-scientific:active {
+    background: var(--button-scientific-active);
+}
+
 .calculator {
     background: var(--calculator-bg);
     border-radius: var(--border-radius);
@@ -306,6 +380,10 @@ BODY {
     background: var(--button-clear-active);
 }
 
+.btn-scientific.pressed {
+    background: var(--button-scientific-active);
+}
+
 /* Improved mobile touch targets */
 @media (max-width: 767px) {
     .btn {
diff --git a/public/index.html b/public/index.html
index eaa7da7..dab3ea2 100644
--- a/public/index.html
+++ b/public/index.html
@@ -8,6 +8,9 @@
   </head>
   <body onLoad="setValue(0)">
     <div class="container">
+      <button class="theme-toggle" onClick="toggleTheme()" aria-label="Toggle dark/light mode">
+        <span class="theme-icon">🌙</span>
+      </button>
       <main class="calculator" role="application" aria-label="Calculator">
         <div id="results">
           <div id="result" role="textbox" aria-label="Calculator display" aria-live="polite" aria-readonly="true" tabindex="0"><span class="digit0">0</span></div>
@@ -16,7 +19,13 @@
         <div id="loading" style="visibility:hidden" aria-hidden="true"></div>
 
         <div class="calculator-buttons" role="grid" aria-label="Calculator buttons">
-          <button class="btn span-2" aria-label="Empty button" disabled></button>
+          <button class="btn btn-scientific" onClick="scientificOperation('sin')" aria-label="Sine">sin</button>
+          <button class="btn btn-scientific" onClick="scientificOperation('cos')" aria-label="Cosine">cos</button>
+          <button class="btn btn-scientific" onClick="scientificOperation('tan')" aria-label="Tangent">tan</button>
+          <button class="btn btn-scientific" onClick="scientificOperation('sqrt')" aria-label="Square root">√</button>
+
+          <button class="btn btn-scientific" onClick="scientificOperation('log')" aria-label="Logarithm">log</button>
+          <button class="btn btn-scientific" onClick="operationPressed('power')" aria-label="Power">x^y</button>
           <button class="btn" onClick="clearPressed()" aria-label="Clear all">C</button>
           <button class="btn" onClick="clearPressed()" aria-label="Clear entry">CE</button>
 
diff --git a/test/arithmetic.test.js b/test/arithmetic.test.js
index deded48..1a774d3 100644
--- a/test/arithmetic.test.js
+++ b/test/arithmetic.test.js
@@ -205,4 +205,88 @@ describe('Arithmetic', function () {
                 });
         });
     });
+
+    describe('Scientific Operations', function () {
+        describe('Sine', function () {
+            it('calculates sine of 0', function (done) {
+                request.get('/arithmetic?operation=sin&operand1=0')
+                    .expect(200)
+                    .end(function (err, res) {
+                        expect(res.body).to.eql({ result: 0 });
+                        done();
+                    });
+            });
+        });
+
+        describe('Cosine', function () {
+            it('calculates cosine of 0', function (done) {
+                request.get('/arithmetic?operation=cos&operand1=0')
+                    .expect(200)
+                    .end(function (err, res) {
+                        expect(res.body).to.eql({ result: 1 });
+                        done();
+                    });
+            });
+        });
+
+        describe('Square Root', function () {
+            it('calculates square root of 9', function (done) {
+                request.get('/arithmetic?operation=sqrt&operand1=9')
+                    .expect(200)
+                    .end(function (err, res) {
+                        expect(res.body).to.eql({ result: 3 });
+                        done();
+                    });
+            });
+
+            it('calculates square root of 0', function (done) {
+                request.get('/arithmetic?operation=sqrt&operand1=0')
+                    .expect(200)
+                    .end(function (err, res) {
+                        expect(res.body).to.eql({ result: 0 });
+                        done();
+                    });
+            });
+        });
+
+        describe('Power', function () {
+            it('calculates 2 to the power of 3', function (done) {
+                request.get('/arithmetic?operation=power&operand1=2&operand2=3')
+                    .expect(200)
+                    .end(function (err, res) {
+                        expect(res.body).to.eql({ result: 8 });
+                        done();
+                    });
+            });
+
+            it('calculates 10 to the power of 2', function (done) {
+                request.get('/arithmetic?operation=power&operand1=10&operand2=2')
+                    .expect(200)
+                    .end(function (err, res) {
+                        expect(res.body).to.eql({ result: 100 });
+                        done();
+                    });
+            });
+        });
+
+        describe('Logarithm', function () {
+            it('calculates log of 10', function (done) {
+                request.get('/arithmetic?operation=log&operand1=10')
+                    .expect(200)
+                    .end(function (err, res) {
+                        expect(res.body).to.eql({ result: 1 });
+                        done();
+                    });
+            });
+
+            it('calculates log of 100', function (done) {
+                request.get('/arithmetic?operation=log&operand1=100')
+                    .expect(200)
+                    .end(function (err, res) {
+                        expect(res.body).to.eql({ result: 2 });
+                        done();
+                    });
+            });
+        });
+    });
 });