Updated Timer

src/Timer.css

@@ -1,17 +1,16 @@
-.app {
+.timer {
   text-align: center;
-  background-color: #282c34;
   display: flex;
   flex-direction: column;
   align-items: center;
   justify-content: center;
   font-size: calc(10px + 2vmin);
   color: white;
+  flex: 1;
 }
 
 .time {
   font-size: 3rem;
-  padding: 2rem;
 }
 
 .button {

src/Timer.js

@@ -1,19 +1,23 @@
-// I used code as basis to this Timer
+// Timer is based on these with changes
+
 // Build a React Timer Component Using Hooks by James King
 // https://upmostly.com/tutorials/build-a-react-timer-component-using-hooks
 
 import React, { useState, useEffect } from 'react';
 
 const Timer = () => {
-  const [seconds, setSeconds] = useState(0);
+  const [startTime, setStartTime] = useState(0);
+  const [elapsedTime, setElapsedTime] = useState("0.0");
   const [isActive, setIsActive] = useState(false);
 
   function toggle() {
+    setStartTime(new Date());
     setIsActive(!isActive);
   }
 
   function stop() {
-    setSeconds(0);
+    setStartTime(0);
+    setElapsedTime("0.0");
     setIsActive(false);
   }
 
@@ -21,25 +25,37 @@ const Timer = () => {
     let interval = null;
     if (isActive) {
       interval = setInterval(() => {
-        setSeconds(seconds => seconds + 1);
-      }, 1000);
-    } else if (!isActive && seconds !== 0) {
+        let epochElapsedTime = new Date() - startTime;
+        
+        let elapsedTime = {
+          minutes: new Date(epochElapsedTime).getMinutes(),
+          seconds: new Date(epochElapsedTime).getSeconds(),
+          milliseconds: new Date(epochElapsedTime).getMilliseconds()
+        };
+        
+        if(elapsedTime.minutes !== 0){
+          setElapsedTime(elapsedTime.minutes + ":" + elapsedTime.seconds + "." + elapsedTime.milliseconds);
+        } else {
+          setElapsedTime(elapsedTime.seconds + "." + elapsedTime.milliseconds);
+        }
+      }, 10);
+    } else if (!isActive && startTime !== 0 && elapsedTime !== "0.0") {
       clearInterval(interval);
     }
     return () => clearInterval(interval);
-  }, [isActive, seconds]);
+  }, [isActive, startTime, elapsedTime]);
 
   return (
     <div className="timer">
       <div className="time">
-        {seconds}s
+        {elapsedTime}
       </div>
       <div className="row">
         <button className={`button button-primary button-primary-${isActive ? 'active' : 'inactive'}`} onClick={toggle}>
-          {isActive ? 'Pause' : 'Start'}
+        {isActive ? 'Pause' : 'Start'}
         </button>
         <button className="button" onClick={stop}>
-          Stop
+        Stop
         </button>
       </div>
     </div>